Theoretically,
the perfect crime could be committed. But every mistake leaves a trace. The
problem with most crimes is that they are not perfectly planned, if at all, and
that too many interpersonal relationships hover in the background. Criminals
often leave traces because they are stressed or get surprised. Besides, rarely
will crimes be resolved based on physical
traces only. Questioning, review of bank accounts or e-mails, as
well as apparently random discoveries also play an important role. This ex post facto combination of at first
seemingly unrelated information turns increasingly into a Big Data task of
recognizing and relating patterns that resolve crimes. The perfect crime remains
possible in theory, but, procedural failings of investigation and trial aside, becomes
increasingly difficult to commit.
We all leave a lot of traces all the time
that stem from virtually every activity we undertake. We shed DNA in an amazing
variety of forms. Just one such example is “touch
DNA,” left when we touch a surface such as a table, similarly to fingerprints
left on surfaces we touch without gloves. Both DNA and fingerprints are often found
at crime scenes. They can identify and place an individual and are usually
considered part of the gold
standard of evidence. But there are also other traces, such as footwear
impression evidence. While they usually lead to a shoe rather than
to an individual, they are especially important in serial crimes such as
burglaries: burglars often wear the very same shoes to different crime scenes,
which allows investigators to make critical connections between cases. A less
well-known type of evidence is fiber
traces, stemming from fibers that are transferred through contact
between fabrics. They allow conclusions to be drawn about the presence of an
individual in a room.
Of course, among the challenges that
remain is figuring out what traces are relevant to solving a case.
Another question is how perpetrators blur their traces. They do this
primarily by trying not to leave any. Shoe and finger marks, hair,
clothing fibers, voice or surveillance camera records and DNA are typically left
at the crime scene by any individual that had contact with the room in the
first place. It is theoretically possible not leave such traces if a person wears
gloves, a jumpsuit or, rather, a full-body suit donned without leaving external
DNA and fingerprints. Still, such an individual’s behavior would have to be timed
very professionally so as not to leave any traces at all. Even very careful
people often overlook trifles: wearing a glove eliminates the risk of touch DNA
but touching one’s face with the glove and then some object in the room still
leaves that individual’s DNA traces behind. So, if traces exist, technologically
savvy criminals seek to clean them up. Such cleanup attempts are often fruitless
because by now, scientific methods exist to visualize concealed traces. Furthermore,
most crimes are neither calculated nor planned but occur out of a poorly
controlled impulse. Mistakes happen easily. Each of them leaves a trail.
Even
“removed” traces can be made visible again, somewhat depending on
circumstances. As an example: blood on a red carpet is not easily noticed at
first sight because of poor contrast. But different
light sources with different
wavelengths can be used to illuminate the rug from different angles.
Blue light, white light, UV light and infrared light are often used to
highlight easily overlooked traces. If blood has dried, it absorbs blue light
and appears very dark, at best it is darker than the surface it is on. Where
light tools are not enough, chemicals may be brought in. As far as traces of
blood are concerned, Luminol
is a well-known chemical that, when sprayed on potential blood stains, reacts
with blood hemoglobin so that luminescence becomes visible: after treatment
with luminol, blood traces shine bright blue. In principle, of course, forensics
first uses optical methods which do not alter the chemistry of the trace.
Only in a second or further round, chemicals are resorted to.
Except
for identical twins, DNA is different from person to person. It exists in every
cell of the human body. Everything we touch, and every bodily fluid we emit,
such as blood, semen, sweat, contains our DNA. It enables individual
identification of a specific person. This is why DNA evidence is often
considered the safest avenue and why it enjoys a reputation superior to
virtually every other type of evidence.
But DNA
can also mislead an investigation. One needs to be careful in assessing
the significance of traces. DNA can lead to a particular person, but it does
not automatically mean that the individual whose DNA ended up at a
place of interest is the perpetrator of a crime.
Speaking
of DNA as a key to Pandora’s box, the mere availability of answers may not
always render it wise to ask the question. One feels reminded of Jack
Nicholson’s immortal dictum in A Few Good
Men: ”You want the truth? You
can’t handle the truth!” Especially when it comes to questions of
legitimacy, DNA evidence raised questions about the descent of the House
of Plantagenet but, multiple-edged sword that it is, appears to have
raised no
fewer questions about the House of
Windsor that has long been beleaguered
by compelling genetic arguments disputing the descent of Queen Victoria from Prince Edward,
Duke of Kent and Strathearn, holding that hemophilia
suddenly appeared in Victoria’s descendants but did not exist in the royal
family before, while porphyria
was prevalent in the family before Victoria (such as in George III) but never
afterwards.[1]
Of course, the mere thought of DNA evidence conveying residency at Buckingham
Palace from Elizabeth II to a character like Ernst August
of Hanover would likely terminate popular acceptance of
legitimacy-based monarchy in Britain.
Another frequently encountered challenge is the determination of the age
of fingerprints. Fingerprints consist mainly of water and lipids
such as cholesterol. To identify a person based on fingerprints, the papillary
lines we see on fingertips that form a fingerprint need to be analyzed very precisely:
where do two lines cross, where does a line end? These details serve to compare
a trace with evidence in databases. But we can also analyze a fingerprint’s
chemical composition. In that process, we learn which substances are
present and in what quantity. These substances change with time, and from this
change one can deduce hypotheses about the age
of a fingerprint.
Current research examines how collaboration
and communication between different actors in the criminal justice system
such as expert witnesses, crime scene investigators, detectives, prosecutors
and judges works, especially regarding DNA, fingerprints and handwriting. Communication
between them is important to enable interpretation of information obtained from
traces that have been secured. DNA and fingerprints have a strong reputation. Handwriting,
however, has come to be considered rather unreliable evidence. This is so in
part because handwriting analysis is frequently confused with graphology. Graphology
intends to explore the writer’s character from his handwriting, but it is not
based on scientific principles. Handwriting
analysis, on the other hand, compares the handwriting in
several documents to determine whether they were written by the same
individual. This process results in a probability statement that can appear
unreliable because the public generally expects an analysis of
evidence to provide close to 100 percent reliability of results. Therefore, it
is often and conveniently forgotten that there is no such thing as any analysis
with 100 percent reliability. Even DNA
testing is based on mere probability statements.
Handwriting analysis is not the only salient
aspect of a written piece. Formation of sentences is no less important. Analysis
starts with sheet design. For example, handwriting experts pay attention to
where an individual starts to write on a sheet of paper, what the top margin
and side margins are, what line spacing is used, whether the entire sheet is
used, and other similar factors. It is true
that handwriting appears to lose
significance in a digitized world, but it maintains an important application in
the analysis of authenticity
of holographic wills.
Scope and methods of forensic analysis have changed
greatly over recent years as technology has taken on far greater importance.
Developments in photography, computer science, robotics or analytical chemistry
simplified many processes. DNA analysis has revolutionized forensics and police
investigations at the end of the 20th century and forensic applications of technology
will continue to evolve. But while technology development is an important focus,
evaluation and significance of analytic results needs to remain the principal focus
of every investigation.
The educational relationship between forensic
science and police investigation is in flux as well. Switzerland
has its own forensic study program at the University
of Lausanne. It conducts international research in forensics and
offers an academic education where students deal with chemistry, mathematics,
physics, and securing and evaluation of evidence. Graduates are qualified as
"general practitioners of forensics." Forensics is a composite science
that supports police investigations. Most European universities
do not offer comparable training. In the
U.S., forensics is also confined to second- and third-tier colleges.
This correlates somewhat with the low priority accorded to Evidence
in the curriculum of leading American as well as European law schools – and
even in bar exams – very likely because the field itself does not lend itself
terribly much to academic theorizing but is extremely important in
practice. Yet it is an indispensable sequitur from burden
of proof. Crime scene work and forensics are police tasks, so research
in this area is mainly police driven, and crime lab staff is notoriously overworked
and underpaid. It would be beneficial if forensics could be
established more broadly as a scientific discipline. One area where forensics
is a firmly established subject of analysis or scholarship only marginally
related to the physical sciences is forensic accounting and valuation,
a function on which I plan to reflect in
a different post at a later time.
Another 21st century facet is emerging with vast speed: digital evidence and digital
forensics. As is the
case with other types of evidence, courts make no presumption that digital
evidence is reliable without some evidence of empirical testing in relation to
the theories and techniques associated with its production. The issue of
reliability means that courts pay close attention to the manner in which
electronic evidence has been obtained and in particular to the process in which
the data was captured
and stored. Earlier
process models have tended to focus on one particular area of digital forensic
practice, such as law enforcement, and have not incorporated a formal
description. The more recent
Advanced Data Acquisition Model contends that this approach has prevented the establishment of
generally-accepted standards and processes that are urgently needed in the
domain of digital forensics. It represents a generic process model as a step
towards developing such a generally-accepted standard for a fundamental digital
forensic activity – the acquisition of
digital evidence.
