Chapter 4: The Origin of Evidence

Transcription

Copyright Robert C. Shaler 2009 All Rights Reserved
3/2/2010
Chapter 4: The Origin of Evidence
In chapter 1, a purposely broad working definition of evidence was proposed as it
pertains to crime scene investigation.
“Anything associated with a crime scene or incident; whether or not it has been
collected, described, photographed, analyzed scientifically or reasoned about and
that may be introduced into a legal proceeding in order to help ascertain the truth
of an issue.”
The purpose of such a broad definition was to bring the concept of evidence out
of its traditional legal realm and into the world of the practicum. In chapter 1, the section
titled “The Concept of Evidence” introduced the idea that evidence is not a simple
concept and that its definition may have a psychological component unrelated to its legal
relevance. Also, the thought was suggested that unrecognized evidence may still be
evidence.
This chapter expands the discussion of evidence as it relates to the scene
investigations beginning with a historical perspective. In this regard, any meaningful
discussion of crime scene evidence must begin with the most well known and perhaps the
founder of modern criminalistics, the French physician and lawyer, Dr. Edmond Locard.
His work embodied the phrase attributed to him, Every Touch Leaves a Trace, which are
also the basic tenet of criminalists and the creed of crime scene investigators.
The Locard Exchange Principle – Every Touch Leaves a Trace
Although Locard likely never said it precisely like that, the Exchange Principle
ascribed to him forms the basic philosophy of and the reason for conducting a crime
scene investigation. Locard’s writings never explicitly mentioned something that he
termed an exchange principle (principe de l’echange) but he did certainly embrace the
concept. For example, writing about the analysis of dust in 1930,1,2,3 he wrote [bold
added]:
“Among recent researches, the analysis of dust has appeared as one of the newest
and most surprising. Yet, upon reflection, one is astonished that it has been
necessary to wait until this late day for so simple an idea to be applied as the
collecting, in the dust of garments, of the evidence of the objects rubbed against,
and the contacts which a suspected person may have undergone. For the
microscopic debris that covers our clothes and bodies are the mute witnesses,
sure and faithful, of all our movements and of all our encounters.”
1
Locard, Edmond, The Analysis of Dust Traces, American Journal of Police Science, 1(3), 1930, 279-298.
Locard, Edmond, The Analysis of Dust Traces (Second Part), American Journal of Police Science, 1(4),
1930, 401-418.
3
Locard, Edmond, The Analysis of Dust Traces (Conclusion), American Journal of Police Science, 1(5),
1930, 496-514.
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Inman and Rudin4 believe Locard’s publications from 1920 and 1923 represent
his “slightly different insights into his thinking on the issue of material transfer.” The
term insights might more properly represent the normal progression one’s mind makes as
it matures with experience. Certainly by 1930, Locard was convinced that microscopic
evidence formed the essence of evidence transfer and, hence, his exchange principle. As
Bisbing wrote5,
“Duayne Dillon recently lamented that authors over the years have offered varying
statements that they identified as "Locard's Exchange Principle" and much has been
made of the importance of this "principle." He noted that Locard's publications make no
mention of an "Exchange Principle," although Locard did make the observation, "Il est
impossible au malfaiteur d'agir avec l'intensit que suppose l'action criminelle sans laisser
des traces de son passage," translated as "It is impossible for a criminal to act, especially
considering the intensity of a crime, without leaving traces of this presence," in the first
sentence in Chapter 3 (Traces) in Manuel de Technique Policière, Paris: Payot, 1923.”
Although Locard likely never explicitly referred to his thoughts or beliefs as an exchange
principle, others did, as Bisbiing also wrote,
“The first reference found of Locard's exchange principle appears in Reginald Morrish's,
The Police and Crime-Detection Today, London: Oxford University Press, 1940, 72. (4)
The Locard Exchange Principle was reiterated by L.C. Nickolls, in 1956, referencing
Locard (1928), thereby confirming it as a lasting principle applicable to forensic
microscopists' work worldwide. (5) I commonly express the principle this way: whenever
two objects come in contact with each other, they transfer material from one to the other.
The Locard exchange produces the trace evidence of interest from fingermarks to mud.”
One might wonder what drove Locard to drive down that specific scientific path.
It certainly was not on the minds of his contemporaries. His education in science and the
law certainly demonstrated that he had an interest and the background to apply science to
the law. Perhaps this juxtaposition of disciplines was the seed that sprouted in his mind.
Interestingly, who influenced Locard the most? He attributes his revelation with respect
to trace evidence’s importance in criminal investigation to two seemingly divergent
historical figures1. He wrote,
“I must confess that if, in the police laboratory of Lyon, we are interested in any
unusual way in this problem of dust, it is because of having absorbed the ideas
found in Gross and in Conan Doyle …”
Hans Gross was a forensic giant at that time, so it is little surprise that Locard
studied Gross’ 1893 Manual for Examining Magistrates6. From Locard’s perspective, this
arguably formed the basis of modern criminalistics, if he thought of it as that, because
this was the first publication describing the marriage among science, the crime scene
4
Inman and Rudin, ibid, page 93-94.
Bisbing, Richard E., Fractured Patterns: Microscopical Investigation of Real Physical Evidence,
http://www.modernmicroscopy.com/main.asp?article=1, 2004
6
Gross, Hans. Handbuch für Untersuchungsrichter als System der Kriminalistik (Handbook for Examining
Magistrates as a System of Criminology), 2 vols., 1893.
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investigation and the law; Locard’s passions. Gross combined, for the first time, fields of
knowledge that had not previously been integrated. As Locard wrote in 1930,
“It would a mistake to believe that the idea of studying dust for the purpose of
discovering criminological evidence is of modern origin. By seeking diligently we
may trace it to the old masters of legal medicine. However, the first author who
clearly described cases where this research has been made is Hans Gross.”
Continuing, he wrote, “In his ‘Manual for Examining Magistrates’ Gross
grouped together everything in these various teachings that would contribute to
the building up of a good criminal investigation.”
Locard’s second historical influence was Sir Arthur Conan Doyle, the author of
The Adventures of Sherlock Holmes. However maybe that really should not be huge
surprise. Doyle was a University of Edinburgh educated physician who learned the art of
analytical reasoning from his professor, Joseph Bell, an army surgeon and hospital
physician. Applying his training to his literary skills, Doyle skillfully applied his training
and acute mind by creating the fictional hero, turning the highly egocentric and
indefatigable Holmes into a master scientific sleuth. As Locard wrote,
“For in the adventures of Sherlock Holmes, the detective is repeatedly asked to
diagnose the origin of a speck of mud, which is nothing but moist dust.”
While the above suggests that Locard was inspired by Gross and Doyle, one
reference7 says, “…Locard himself referred to a German chemist (Liebig) for his initial
ideas.” Regardless of whether it was Gross, Doyle or Liebig, they, however, were not the
only well known forensic investigators – criminologists as they were called at the time –
that influenced Locard. Clearly, his high opinion of Gross affected him greatly, but
Locard lived in Lyon and Gross was in Prague. A close and early association in Lyon was
a heavyweight criminologist in the early 1900’s, Alexandre Lacassagne, the founder of
the Lacassagne School of Criminology and a major force in criminal investigations in
Lyon. One might speculate that Locard’s disillusionment with Lacassagne, if that is what
it turned out to be, might be that Lacassagne was a devotee of Gall’s theories about
phrenology, a defunct trade once thought to be a science. Did Locard recognize that
phrenology was fraudulent? If so, would that have been sufficient enough reason for him
to look more askance at Lacassagne?
After passing the bar exam in 1907, Locard traveled to Paris to study with
Alphonse Bertillon, the founder of the first scientific method for identifying criminals –
anthropometry, commonly known as Bertillonage. Like Locard, Bertillon was a forensic
renaissance man who dabbled in numerous forensic arenas and believed fervently in the
application of science to criminal investigation. It seems surprising, then, that Locard
failed to mention Bertillon as someone who helped shape his beliefs with respect to the
transfer of evidence. Perhaps Bertillon never considered the topic or they never discussed
the subject or Bertillon didn’t believe it was important. Bertillon did go to crime scenes
7
Robertson, James and Claud Roux, 5.1, From the Crime Scene to the Laboratory, in Forensic
Examination of Fibres, 2nd Edition. Editors James Robertson and Michael Grieve. CRC Press, 1999, page
89.
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and, as Bertillon’s student, Locard would have benefitted from his mentor’s belief in the
application of science to the investigation of crime.
The Origin of Evidence - Divisible Matter
Although not expressed explicitly, the concept of the Exchange Principle
attributed to Locard was certainly entrenched in his mind and demonstrated in his work.
Inherent, too, in his belief that microscopic evidence could be transferred between and
among people and between and among inanimate objects, such as a crime scene, was that
such transfers required energy. Locard believed that it was the nature of a violent crime to
provide the force necessary to affect an evidence transfer. Thus, a fiber from a sexual
assault victim’s blouse would undergo a force such that when an assailant’s shirt rubbed
against it, it would come loose and transfer to the assailant’s shirt. Similarly, for example,
fibers from the assailant’s shirt would transfer to a victim’s blouse. For Locard, the
operative word was “force,” which implies energy. He believed it required energy to
make such transfers happen. However, the theory may not explain reality. For example,
certain fabrics “give up” their fibers easier than others. Thus some fabrics require more
energy to release fibers than others. If the energy isn’t there, transfer may not occur. Still,
Locard’s ideas represent the reality of what forensic scientists observe in the laboratory
today.
Inman and Rudin8 accepted Locard’s idea that it takes energy (force) to affect
evidence transfer. They made it what they refer to as one of two guiding principles
concerning the generation of evidence: Divisible matter and transfer (Locard’s Exchange
Principle). For them, divisible matter implies a source of energy. They argue that
something happens to evidence (their premise is that it is not evidence until this happens)
which gives it the ability to transfer. They call this a “fracture9” which requires energy.
Once transferred, however, they define this transferred material as evidence, whether
discovered or not. As they wrote10,
“If the crime is never discovered or the evidence is never detected, matter
has still divided and transferred, and traits have still transferred.”
They argue that the transfer occurs with only certain kinds of evidence, excluding
impression and physical match evidence. They write that Locard’s transfer principle may
not explain these types of evidence.11
“Recognize that divisible matter does not account for a large category of
evidence, that of pattern transfer evidence, such as prints and impressions. The
transfer of matter requires its prior division; the transfer of ‘traits’ may not.”
Defining a new fundamental principle while excluding a large category of
evidence types, a priori, seems problematic. If it is really is a new fundamental principle
8
Inman and Rudin, ibid, chapters 3 and 4, pages 75-99.
Inman and Rudin, Ibid, page 87.
10
Inman and Rudin, ibid, page 78.
11
Inman and Ruding, ibid, page 77.
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of forensic science, one should expect it to apply to all evidence, regardless of type.
Otherwise, it is not fundamental. Logically, then, Inman and Rudin would require each
subcategory of evidence to have its separate fundamental principle. When Inman and
Rudin discuss impression evidence, they state12:
“Although small amounts of physical matter may be transferred, it is the pattern
of transfer that concerns us, not the substance. Therefore divisible matter does not
apply.”
Irrespective of whether it is a fundamental principle, criminalists are concerned
with the transfer of the pattern or trait that may have identification potential because of
the individualizing characteristics present. However, pattern evidence is created because
a division from the original takes place, which requires energy, and it occurs regardless of
whether the transferred pattern has individualizing characteristics. The mechanism is the
same. It requires energy. In fact, Locard would likely disagree that the “substance”
transferred has little or no value. As Locard wrote when he described a case13 in which
the pattern (trait) itself had little individualizing value,
“The silverware of a restaurant had disappeared. Whoever had taken it must have
mounted a chair in order to reach the shelf where it was kept. As chance would
have it, there was on the seat of the chair a forgotten napkin. A shapeless mark
had been left on the napkin, not distinct enough to indicate the kind of shoe worn
by the individual. There was, however, a trace of mud on it, and this was
examined under the microscope. In the midst of various animal and vegetable
waste matter, there were discovered a superabundance of fine granulations which
were recognized as fecal material. This fact was a reminder that during the same
night scavengers had been working in a neighboring alley. Consequently, the
investigation was directed to these men.”
Fingermark evidence is also a category of pattern evidence for which there may
be sufficient individualizing characteristics to make specific identifications. However,
that does not imply that the only value of a latent print is to make identifications.
Fingermarks come from people, and while it may not take much energy to divide the
fingerprint residue from a finger to a physical substrate, there is certainly a division
process that takes place of not just the pattern but also the constituents of the print itself.
These constituents have investigative value. For example, recent work by Leggett et al,
which they term “lifestyle fingermarking,” suggests that drugs and drug metabolites can
be identified from fingermarks14. Additionally, if during commission of a crime, a
perpetrator strangles the victim and then subsequently touches a surface, the epithelial
cells of the victim would be associated with the perpetrator’s fingermark. By limiting
one’s criminalistic activities to simply identifying who left the print, a valuable source of
information would be missed.
12
Inman and Rudin, ibid, page 98.
Locard, Edmond, ibid, page 509.
14
Leggett, Richard, Emma E. Lee-‐Smith, Sue M. Jickells, and David A. Russell, Intelligent Fingermarking: Simultaneous 13
Identification of Drug Metabolites and Individuals Using Functionalized Antibody Nanoparticles. Angew. Chem. Int. Ed. 2007, 46, 4100 –4103
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In the context of the concept of divisible matter, the following illustrates two
transfers. First is the transfer of the victim’s skin cells to the hands of the perpetrator.
This requires energy and the removal (dividing/fracturing) of the victim’s epithelial cells
from her neck. The subsequent transfer is called secondary transfer (discussed below)
where the victim’s epithelial cells are then transferred to another surface. Both transfers
invoke the principle of divisible matter.
It seems, then, that defining divisible matter should not be so restricted because as
science advances, the potential exits that a class of evidence not seemingly following
Inman and Rudin’s definition of divisible matter may convert to one that does. Their
definition,
“Matter divides into smaller component parts when sufficient force is applied.
The component parts will acquire characteristics created by the process of
division itself and retain physicochemical properties of the larger piece.”
The division of matter is shown schematically below. The original source of the
evidence comes from the participants in the crime – the scene, the victim, the perpetrator
– and the divided evidence goes in two directions, each exposed to varying and likely
different influences.
From the concept of Divisible Matter, Inman and Rudin describe three corollaries which
they believe follow logically:
“Corollary 1: Some characteristics retained by the smaller pieces are unique to
the original item or to the division process. These traits are useful for
individualizing all pieces to the original item.
Corollary 2: Some characteristics retained by the smaller pieces are common to
the original item as well as to other items of similar manufacture. We rely on
these traits to classify the item.
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Corollary 3: Some characteristics of the original item will be lost or changed
during or after the moment of division and subsequent dispersal; this confounds
the attempt to infer a common source.”
Evidence Dynamics
Corollary #3 considers once division (fracture) has taken place, the uncertainty of
a new environment intercedes. This concept was first espoused by Chisum and Turvey15
in their concept of Evidence Dynamics,
“The process of crime reconstruction is often built on the assumption that
evidence left behind at a crime scene, which has been recognized, documented,
collected, identified, compared, individuated, and reconstructed is pristine. This
assumption involves the belief that the process of taping off an area, limiting
access, and setting about the task of taking pictures and making measurements
ensures the integrity of the evidence found within. Subsequently, any conclusions
reached through forensic examinations and reconstructions of that evidence are
assumed to be a reliable lens through which to view the crime. This assumption
is not always accurate.” [bold added]
Evidence dynamics refers to influences that “changes, relocates, obscures, or
obliterates physical evidence, regardless of the intent.” Generally, the process involved in
evidence dynamics begins at the instant that a force interacts with evidence to cause a
transfer until it reaches the courtroom. The thought that the process ends there is not
necessarily true, either, as evidence used or not used in a legal proceeding may be
required for subsequent hearings or trials. Each time the evidence is used, the potential
exists for it to change or be obliterated, a process can continue until it is finally destroyed
under some authority.
Chisum and Turvey list several influences on Evidence Dynamics and caution
that each should be considered when evidence is examined. Their list, while seemingly
comprehensive is not meant to be all-inclusive. Schematically, evidence dynamics may
look like the following.
15
Chisum, Jerry W. and Brent E. Turvey, Evidence Dynamics: Locard’s Exchange Principle & Crime
Reconstruction. Journal of Behavioral Profiling, January, Vol 1(1), 2000,
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Here, the evidence can go in one of two directions, one with the participants of
the event and the other remains with its original source, each subjected to a new
environment - wear, the environment, interaction with chemicals – with the potential for
obliteration and/or contamination. The following lists those influences they considered.
While it should not be necessary to discuss each of the above, these must be prime
crime scene considerations, and investigators should be cognizant that these influences
exist and actively consider whether any of these might have affected the evidence at the
scene. If so, then appropriate action should be discussed and implemented. The
implications are abundantly clear. Although Chisum and Turvey were writing specifically
about crime reconstruction, scene scientists/investigators must understand the resultant
effect they can have on the investigation, reconstruction not withstanding.
“The failure to consider Evidence Dynamics as a part of any crime reconstruction
has the potential to provide for misinterpretations of physical evidence, and
inaccurate or incomplete crime reconstruction.”
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Students and beginning investigators should consciously consider the effect
extraneous forces have on evidence. In fact, they should actively not only be aware of the
above, but consider the ramifications that each might have on an investigation.
Crime Scene Elements
Before considering evidence transfers in more detail, what follows is a general
discussion of the interrelated components of a crime scene as they relate to where
evidence may be found and the microenvironments within those areas. In essence, then,
this focus is on those sub-scenes within the larger context of the whole.
The general concept behind finding probative evidence is “Evidence Leads to
Evidence.” Many crime scene texts ignore this topic, except as a passing comment on
searching. Instead, they focus on the various classes of evidence – trace evidence,
impression evidence, DNA evidence, and etc, - without considering the necessary
preamble to the discussion that puts all evidence into perspective. This is an oversight
because understanding the sub-context of evidence is the critical underlying thought
process behind locating it, the fundamental reason for conducting the crime scene
investigation. It dictates whether the investigation will be successful.
In their text, Lee, Palmbach and Miller16 consider the subject tangentially, briefly
discussing microscopic and macroscopic aspects of crime scenes. The sum total of their
discussion with respect to the macroscopic point of view is with respect to a scene they
described earlier in their text.
“The macroscopic point of view of the crime scene above would include not just a
location, but the victim’s body, the suspect’s body, the houses, and the vehicle
involved. Essentially, this definition is looking at variously sized crime scenes
within a crime scene – all are important and should be treated and investigated as
crime scene.”
They only mention that such a thing as a microscopic point of view exists in the
following,
“… any specific object or piece of physical evidence related to the crime being
investigated.”
This is a critical concept that is being ignored or considered lightly. Scene
scientists/investigators and students need to understand that a scene, in reality, is many
scenes within the whole. Each element of which is a sub-scene unto itself called either
microscenes (microscopic) or macroscenes. Students and scene scientists/investigators
must understand this concept. They are entirely interrelated and form the basis of a
holistic approach to a competent and complete scene investigation.
16
Lee, Henry C., Timothy Palmbach and Marilyn Miller, ibid, page 4.
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The Macroscene
The macroscene is what an investigator sees on entering the scene, whether a
homicide or a burglary. It is what assaults the visual, olfactory and psychological senses
through the assimilation of a plethora of sensory stimuli. A homicide scene may have a
body, a pool of blood, obvious signs of a struggle and spattered blood. A sexual assault
may have evidence of a break-in, rumpled bed sheets and blood. A burglary may have a
broken window, a jimmied door, `or an obviously disturbed jewelry case. A stalking case
may have impression shoeprints outside a window. Depending on the scene, the
macroscene is the investigator’s first visual impression.
This author’s first scene was almost 40 years ago in a dark alley outside a bar in
Pittsburgh. It’s a scene that is not a constant memory, but it is easily brought to the
surface inside the mind. A young woman, lying face up, had been rendered
unrecognizable by a large rock, her face bashed in and turned into a fleshy pulp of blood,
tissue and bone, her blood and brains spilling onto the gravel. There was no odor, just the
mess of a face. After literally hundreds of scenes later, that scene still lives; it never goes
away. The purpose of mentioning this is that our senses are easily assaulted and
overwhelmed. So it is easy to lose focus.
The following scene diagram, a mock shooting incident, was an in-class exercise
for students. First consider the obvious listed on the diagram – the macroscene elements:
A body, a bullet hole in a window, blood on the entrance doorknob on the exterior
surface, blood trail on the floor and small, what might be considered high velocity
spatters on the floor to the right of where the blood trail begins. The gunshot wound to
the deceased is hidden because of his position on the floor although a pool of blood has
formed under him suggestive of what might have happened.
Although the macroscene includes obviously visible aspects, other macroscene
elements are a bit more subtle, although defined for this discussion as part of the
macroscene. The reason is many elements can be made visual by employing simple
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techniques. For example, the window has sub-macroscene elements, the bullet hole being
the most obvious. Others might include features (elements) that do not immediately stand
out: fingermarks on the windowsill, shoeprints in dust on the pavement underneath the
window, forehead and/or fingermarks on the glass from pressing against the window.
These evidentiary elements of the window’s sub-scene, its macroscene, are critical in
understanding the window’s role in the context of overall essence of the scene. They, too,
are part of the macroscene and must be defined as macroscene elements because they can
be easily visualized using common scene investigative tools – ALS, flashlight, etc.
The body is another part of the macroscene, a macroscene element. Dead bodies
can evoke a visceral response in people and because of that they tend to become a focal
point of an investigation and may become the macroscene, to the exclusion of everything
else. This is a natural reaction but should not overshadow the other elements of the
macroscene. Like the window, the body has its own set of macroscene elements:
bloodstains and bloodstain patterns on clothing that are both visible and interpretable,
gunshot residue in the form of fouling or stippling on the skin, contusions and sharp force
wounds, and etc – some of which will be defined by the medical examiner during the
autopsy.
The criminalist investigator must consider each element of the macroscene both
individually and as a part of the whole. A schematic of macroscene elements is shown
below.
While not an all-inclusive list of possible visible and visualized elements,
criminalists should consider these with respect to the scene under investigation.
Considering the scene diagram presented above, the important investigative questions
seem obvious: What is the direction of the bullet - was its path going inside the house? If
so, where is it? Did investigators miss bullet defects? Was the bullet through the window
the fatal shot? Where was the shooter? If the bullet path was leaving the house, where is
it? Where is the gun? What was the target?
The macroscene can be overwhelming. The problem is that the most visual
macroscene elements may be so grossly visual that other, more subtle macroscene
elements are ignored or minimized. For this discussion, the macroscene, while mostly
visible, also includes evidence that is invisible to the naked eye but can be made visible at
the scene. Thus, a fingermark on a door jam that is invisible until dusted is an element of
the macroscene. A dry residue shoeprint in the entry foyer is made visible using oblique
lighting and, too, is an element of the macroscene. These are only examples of
macroscene elements, all of which typically consume much of the energy, thoughts and
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time of crime scene investigators. The evidence that comprises the macroscene might be
defined as:
The macroscene is the individual, visible elements or sub-elements of the crime
scene, where a macroscene element is defined as evidence associated with the
macroscene.
The Microscene- Trace Evidence or Locard Elements
While macroscene elements are visible or can be made visible at the scene,
another, equally important class of evidence is not visually apparent and is likely not be
made visible at the scene. Nevertheless, it holds no less importance for the investigation
and like macroscene elements it must be collected and preserved. These are the
microscene elements, those tiny, microscopic traces transferred during the activity that
results in the crime scene. Scene scientist/investigators classify microscene elements as
trace evidence; however, they may also correctly be considered Locard Elements, in
honor of the scientist who considered them so critical in crime investigation. They
represent the traces, the dust, that likely consumed much of Locard’s attention and which
formed the basis of his thoughts about the transfer of evidence.
The line between macroscene elements and microscene elements is not a clearly
defined cut off. For example, a hair that is visible on a victim’s clothing might correctly
be considered a macroscene element. However, that hair might not be so easily visible,
depending on color, size, location and background contrast, and it might rightly be
thought of as a microscene element. Such restrictive definitions are not as important as
the concept and how it is employed at the scene.
The difficulty in locating and collecting these microscene elements lies in the fact
that they are invisible; collecting them requires diligence and a systematic and logical
approach. It also requires thought about which macroscene elements should be present,
given the scene and the crime, and the type of trace evidence – microscene elements associated with them. For example, the scene diagrammed previously has several
macroscene elements: body, blood trail, bullet hole, etc. Associated with each
macroscene element are microscene elements - trace evidence. Fortunately, there are
standard collection techniques. In order to properly investigate the macroscene elements
at a scene, investigators must consider all of the microscene elements there.
It must be absolutely clear that there is an integral relationship between the macro
and microscenes because the creation of one, by definition, creates the other; the
microscene being the consequence of the activity that created the macroscene elements.
For example, a struggle between two people might result in one of the two ending up
dead. The body is only one element of the macroscene, but it has macroscene subelements (bloodstains, knife wounds, contusions, etc.) and microscene elements (hairs,
fibers, fingermarks, GSR, etc) as well. The knife lying next to the body at the scene is a
macroscene element, with a subset of macroscene elements (blood, fingermarks, hairs,
etc.) and associated microscene elements (fiber traces, DNA, etc.). Schematically, the
microscene might be thought of as:
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The diagram above illustrates the obvious interrelationship between the
macroscene and the microscene, the macroscene the visible and the visualized elements bodies, bullets, etc and the microscene - anything microscopic, such as dust, hairs, fibers,
DNA, etc. In this regard, one might define the microscene as:
The microscene is the microscopic elements associated with the macroscene. It is
typically thought of as trace evidence or Locard Elements. A microscene element
is anything microscopic that can be considered evidence.
It seems obvious, now, that when two participants interact, such as in a violent
crime, physical material will transfer from one to the other and also to the location where
the activity takes place, the scene. This is the theory, but to what extent does this really
happen? Can a transfer happen a second or more times? What evidence (debris) is
normally present in that area of the macroscene? The first question harkens back to the
discussion above with respect to the energy it takes to transfer, say, fibers from one
garment to another during the commission of a crime.
Cwiklik17 considered the second question that refers to a phenomenon called
“secondary transfer” and how often it occurs and what the effect of such transfers might
have on an investigation. [Bold added]:
“…particles and fibers abraded, flaked, broken, or torn from the items themselves
as well as other particles and fibers that have collected on the surface of each
item prior to their contact. The latter particles and fibers are non-component
debris: not an intrinsic (component) part of the items themselves. Their transfer
is referred to as secondary, tertiary, and higher degrees of transfer: indirect
transfer from the source item.”
Cwiklik also considered the third question and defined sets of microscene
elements (the author’s terminology applied to her discussion) intrinsic and exogenous to
macroscenes. She placed them into specific categories, defining each. The following
diagram was adapted from her discussion.
17
Cwiklik, Chesterene, an Evaluation of the Significance of Transfers of Debris: Criteria for Association
and Exclusion. J. Forensic Science, 44(6), 1999, pages 1136-1150.
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The macroscene elements (evidence) are divided into families. Each family
comprises a set of debris (particles and fibers) and an associated sub-set of debris
(particles and fibers). There are also stray particles and fibers and small sub-sets that hold
little investigative value. Each set shares a common condition, such as a common site, a
means of production and a means of transport. As such, they represent a record of the
daily life of that specific macroscene environment.
The sub-sets within each set occur from a diverse set of origins including hairs
and skin flakes from the occupants, fibers indigenous to that specific environment, e.g.,
feathers from pillows in a bedroom or carpet fibers, clothing fibers, e.g., from a
wardrobe, processes that occurred elsewhere, e.g., debris shed from clothing or footwear,
and aerial transport, e.g., soil, traffic dust, insect parts, botanicals such as pollen and/or
spores. These, too, represent part of the daily record of the macroscene.
Different from these is a sub-set of debris that occurs from occasional events
and/or visitors. These represent microscene elements that define a time-line for the events
that took place within that macroscene. Thus, examining a single macroscene
environment at a crime scene will define two important facts: the daily record of that
environment and a time-line of transient events that took place within that environment.
Scene scientists/investigators must be cognizant that each microscene holds such
potential and tailor the search and recovery of evidence so that such information is not
lost. The challenge is recognizing the daily record from the transient record.
The Probability of Macroscene and Microscene Element Transfers
Before a practical discussion on how easy or difficult it is for evidence to transfer,
the topic of how much in the world is there that can be transferred that is found normally
in the environment and is not there because of a crime. Suppose, for example, that you
shake hands with someone and then that person visits a friend. The two friends end up in
an argument and a murder takes place – the friend visited is dead. What is the probability
that your DNA can end up on the murder weapon left at the scene? If the fingermark on
the murder weapon is smudged, that is, not useable with respect to ridge detail present, it
would have your DNA as the only evidence linking someone to that murder. The
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following discussions focus on the likelihood of either primary or secondary transfer
taking place.
Primary Transfer
The Locard Exchange Principle explains the transfer of evidence from one person
to another. There are, however, instances, such as those suggested above, when transfer
does not easily or ever take place. Consider footwear impressions at a scene as an
example. Some footwear impressions fall into the macroscene element category because
they are either immediately visible – wet origin impressions – or are latent but can be
made visible – dry origin impressions. Footwear impressions that must be taken to the
laboratory in order to be made visible are, by definition, microscene elements. For this
evidence to be transferred, the shoe and the receiving surface characteristics must be
appropriate to the production of impression evidence. This means that not all surfaces
will adequately receive impression evidence. Bodziak 18 discusses this in his
comprehensive text on footwear impression evidence. The following diagram, which has
been adapted from Bodziak, illustrates this for footwear evidence.
From the chart above, it is clear that certain surfaces have a higher likelihood of
accepting footwear impressions than others. For example, a wet shoe will likely leave a
print on most surfaces except a carpet. A dry shoe with dust will not likely leave a print
on a floor that is already dirty, and a clean dry shoe will not likely leave detectable prints
on a dirty floor, a carpet or a clean unwaxed floor. So, while Locard’s Exchange Principle
theoretically ensures a transfer of evidence, there are practical considerations with respect
to evidence transfer.
For fibers, Pounds and Smalldon19 and Kidd and Robertson20 showed that the
number of fibers transferred depended on a number of factors, most of which make sense
and others that a priori do not.
18
Bodziak, William J. Footwear Impression Evidence – Detection, Recovery, and Examination. CRC Press,
New York, 2000, pages 17-20.
19
Robertson and Roux, ibid, pages 89-90.
15
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The surface area in contact
The number of contacts
The force/pressure applied during contact is directly related to the number of
fibers transferred up to a maximum number.
The pressure causes fragmentation of the fibers resulting in the preferential
transfer over larger fibers
Cotton, acrylic or wool fibers transferred easier than polyester or viscose fibers,
with 80% of the polyester or viscose fibers transferred were less than 5mm.
Differential shedding was exhibited during fiber transfer21. That is, Fibers in
mixed blends are not transferred in proportion to the stated blend (weight) of
fibers present.
Most fibers in blends transferred the minor component of the blend.
Morphology and thickness of fibers affects transfer.
Some microfibers transfer larger numbers of fibers than cotton, while others do
not transfer as well.
Age and/or wear affects fabric transfer
The above may seem esoteric, especially to those crime scene investigators not
familiar with the concept of fabric/fiber transfer. However, crime scene investigators
should understand and examine, at the scene if possible, the composition of fabrics on
furniture obviously involved in a struggle and on a deceased in order to attempt to
ascertain the potential for the primary transfer of fibers from the crime scene/victim
to a perpetrator during a violent event. This could be critical because favorable
shedding fabrics represent a source of fibers that can transfer to the clothing of an
assailant and which the crime laboratory analyst can often successfully find and
examine. From a cooperative perspective, this is important because it makes the crime
laboratory scientist and the scene criminalist/investigator partners in the investigation.
Another type of multitasking evidence is glass. When glass breaks, fragments or
chards can be spread in a 180 degree variable pattern. Glass fragments occur
backward and forward of a blow, say, to a window. Fragments of both can be found
on, for example, a burglar’s clothing. The following illustration was adapted from
Pounds and Smalldon22.
20
Robertson and Roux, ibid, page 90.
Robertson and Roux, ibid, page 90.
22
Pounds, C.A. and K.W. Smalldon. The distribution of glass fragments in front of a broken window and
transfer to individuals standing nearby. J. Forensic Science Society 18 (1978) 197-203.
21
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Thus, for a burglar breaking a window in order to enter a residence, small shards
of glass should be found in his clothing. Fragments will be found in a 180 degree
semicircle in the area where the window breaks to a distance of up to ten feet, with
most within approximately 3-5 feet of the break. Also, the highest distribution of
fragments would be expected in the area of 45 degrees on either side of the break.
The higher the impact, the smaller the fragments will be. These fragments will have
extremely sharp edges and should imbed themselves easily in clothing or on the soles
of shoes.
From a scene perspective, the investigation team should attempt to determine the
radius of the distribution pattern and where the highest density is located. Within this
area of density, a void patter might be found, which would alert the criminalist of the
size and distribution of potential glass fragments that might be found on the clothing
taken from a suspect. Representative samples should be collected so that an
appropriate comparison can be made.
In an in-class experiment, students broke double-pane basement windows using a
hammer and then tracked the glass shards on both sides of the break. The floor was
taped into sections, 4 with the direction of the force and 4our behind. The shards
traveled at least 10’ in both directions. The students also charted the number of shards
on each side of the break. The following diagram shows their results.
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Secondary Transfer
Secondary transfer reflects the transfer of trace evidence, fibers for this
discussion, from a primary target to a secondary target. That is, a primary transfer has
already taken place from one fabric to another – garment 1 to garment 2. If the
receiving garment, garment 2, comes into contact with another receiving, garment 3,
and fibers from 2 are transferred to 3, some of the fibers that originated on garment 1
are now on garment 3. This is secondary transfer, and has been the subject of
conjecture and laboratory studies for several years. Much of the work has been in the
form of mock situations and much of it relates to garment-to-garment transfers, but
casework examples exist.
From a crime scene perspective, it cannot be lost on the investigator that a
secondary transfer is possible and may have occurred from the victim of a crime to
the perpetrator. No one who works and lives in our modern society is likely to be
completely insulated from others. In fact, it would be unusual, indeed, to find such an
individual. It is possible to envision how fibers might be transferred from one
garment to another in random fashion daily as you move from place-to-place, sit on
various chairs and surfaces that other people have occupied. It would be ludicrous to
think that we are not picking up something from places and objects from where our
lives take us. After all, isn’t this the Locard Exchange Principle? In fact, we are a
walking history of our daily lives. So, if someone attacks us in our homes and there is
physical contact between us and our assailant, there will be a transfer of fibers and
other trace evidence to that assailant. Some of these transfers may involve secondary
or higher transfers.
If we consider the transfer of Locard Elements as axiomatic, it is their persistence
that should be our main concern.
The Persistence of Locard Elements
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Several studies have been done concerning the persistence of fibers. That is, the
time that transferred fibers may remain on a particular surface after transfer during a
crime.
Putting it together.
Let’s examine a case to illustrate, in a simple way, how the origin of evidence can
be thought of from a more practical sense. Consider the following case.
Scene Scenario
Assume you are the crime scene reconstruction supervisor, and your crime scene
unit was dispatched by the prosecutor’s office as a secondary responder in the
investigation into the death of a 45 year old man found shot in the head inside his vehicle.
The vehicle was at the end of a dead-end alley but had been taken to the police
department vehicle processing garage, where your team was to examine it. The police
believed the shooting was a homicide and had started the investigation. The following
facts are relevant:
• The victim had been removed by EMS before the first responding crime scene
team had arrived.
• Bloodstains are on the seat and on the console (photos below the blood patterns
present). They suggest the victim was in the driver’s side of the car when he died
- the largest pool of blood is in the driver’s seat. This was confirmed by the EMS
supervisor, whose team removed the decedent from the driver’s side of the car.
•
•
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•
•
•
•
The windows were up and the doors were shut and unlocked.
The seats are microfiber acrylic.
The autopsy shows a single gunshot to the head with the entrance just behind the
right ear. The projectile had an upward path and did not exit.
The weapon was not recovered at the scene.
Deceased was found slumped over the console with blood dripping onto the
console.
A witness saw an individual inside the passenger’s side of the car. He did not hear
the gunshot.
The passenger’s side door was removed by the crime scene unit.
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During the original scene investigation and after it was secured, the information
above was ascertained. The primary investigative questions should have been apparent,
the most important being:
•
•
•
Was the manner of death: homicide, suicide or accident?
Was the car the primary or only scene – was this staged?
If the manner of death was a homicide, where was the origin of the fatal bullet or
where was the shooter sitting?
Other investigative questions should become apparent as the investigation
continues and as long as questions continue popping up, the investigation is not over.
However, answering a continuous line of questions may take the investigation along
different paths. In this instance, the most important investigative question concerns the
manner of death, which is critical because the truth may be different than how the scene
appears. If it is assumed to be a suicide, the medical examiner will become the prime
investigator. The scene investigator must consider these questions as a routine. Students
have difficulty formulating investigative questions, perhaps because they seem to cloud
those that are more important or that some questions seem to have no immediate answers.
Consider the manner of death. Although this is the function of the ME, the scene
investigator should be thinking manner of death as well. In this instance, the weapon is
missing, which leads to the most obvious conclusion that the case is a homicide. Working
though the questions are important but evaluating the scene for what it has to offer can
often answer seemingly evasive questions. In considering the scene, the scene scientist
should be thinking along the following lines.
•
•
•
•
What are the important macroscene elements?
What microscene elements are critical to this investigation and where are they and
with which macroscene elements are they associated?
Which crime scene investigative techniques are necessary to answer the
investigative the most important questions?
What is missing?
Let’s consider the first two separately. As defined above, macroscene elements
are the most visible elements of the scene. Here, it is the car, which can be split into the
outside and inside. Inside, other macroscene elements might include the seats and the
blood. Outside, the microscene elements become important.
Each macroscene element should be considered separately and logically. In this
regard, a working hypothesis of a possible crime type should be used as a starting point.
In this example, by considering the death either a suicide or an accident would be a
mistake because that would make all external macroscene elements and associated
microscene elements irrelevant. However, by assuming the death is a homicide, whether
it is or not, requires the investigator to be concerned with all external macroscene and
microscene elements, such as fingermarks on the driver’s and passenger’s side doors and
windows.
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The most visible macroscene elements inside the car are the seats, the steering
wheel, the dashboard and the blood. Each must be considered for associated microscene
elements having potential value to the case. The seats, front and back, require an
interesting thought process. Generally, if they are microfiber construction, they might
accept and shed fibers readily. This means investigators should collect exemplar fibers
but also tape lift the seats for hairs and transfer fibers from an unknown assailant. Keep in
mind that the EMS unit has already been inside the car, which means that fibers from
their uniforms and their hair might be present. Exemplars from the EMT’s should be
taken at a later time.
Still considering the death a homicide, an investigator should consider whether
that a struggle took place inside and possibly outside the car. Thus, footwear prints may
be a third macroscene element outside the car. There may be microscene elements on the
victim’s clothing. The deceased’s clothing should be transferred from the ME to the
crime laboratory so that a criminalist can examine them for blood, saliva, fibers and hairs.
Other macroscene elements, such as the dashboard or steering wheel should be examined
for biological evidence. An ALS may help locate possible saliva and/or blood that might
be the assailant’s. Fingermarks on the dashboard and the passenger’s side door are other
microscene elements may possibly be present.
This example is purposely simple, but provides a glimpse of how the investigation
should proceed logically from a macroscene element to its associated microscene
elements. Interestingly, the car scene above turned out to be a suicide, but the
investigative process and questions used at the scene correctly approached the scene as a
homicide. During the real-life investigation, investigators considered the scene a
homicide but dismissed the possibility of a suicide by misinterpreting the blood evidence
inside the car.
21

Chapter 4: The Origin of Evidence

Transcription

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