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Forensic Science and Technology
By Robert E. Gaensslen, Professor, Director of Graduate Studies, Head of the Program in Forensic Science,
University of Illinois at Chicago
Dr. Gaensslen (Ph.D., Cornell, 1971) is an expert in biological evidence examination, DNA
forensic technology, and forensic laboratory approaches in the criminal justice system. He has
coauthored seven books, coauthored nine chapters in edited volumes, and published over 60
papers in the refereed scientific literature. He has also organized, coordinated, and participat-
ed in dozens of workshops and training courses for forensic science laboratory and law enforce-
ment personnel. Dr. Gaensslen is a fellow of the Criminalistics Section, American Academy of
Forensic Sciences. He has received the Paul L. Kirk Distinguished Criminalist Award from the
Criminalistics Section and was made a distinguished fellow by the Academy in 2000. He is a
life member of the Northeastern Association of Forensic Scientists.
I assure you that we are returning to the macro level for the next half hour. Within the
field of forensic science, criminalistics can be organized according to the kinds of
evidence examined in a crime lab. Using this scheme, let me sort the field into chem-
ical, biological, trace, and pattern evidence.
Instrumental analysis is deeply interwoven with the analysis of chemical, trace, and bio-
logical evidence. Forensic investigators who are analyzing materials from a crime scene
typically have three goals: classification, individualization, and reconstruction. They are
particularly interested in establishing the uniqueness of a piece of evidence. People in
quality control think about how to make things the same, but I don't know anyone else
who works on materials who thinks about how to render things unique!
With chemical evidence, the basic task is to
identify a material. What is this, and how
much is there? Chemical analysis can be
further broken down into two categories:
elemental analysis and organic compound
analysis. Both are particularly dependent
on instruments. A good example is identi-
fying gunshot residue. Gunshot residue
can consist of smoke, debris, foreign parti-
cles, or other substances. These materials
are emitted by a gun and are deposited on
the hand of the shooter or on anyone or
anything else in the vicinity. Law enforce-
INSTRUMENTATION FOR A BETTER TOMORROW 43
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ment personnel are very interested in the analysis of
gunshot residue in the hope that the results of such an
analysis will show that someone fired a weapon.
Unfortunately, even if the identification of gunshot
residue is rigorous, it does not prove that the hand fired
the weapon--only that the hand was in the vicinity.
In the 1970s many forensic labs became interested in a
The identification technique known as neutron activation analysis to iden-
tify materials. But it proved less useful than anticipated.
of organic The cost and difficulty of the technique were part of the
problem, and it promised more than it could deliver.
There were so many variables associated with the ele-
compounds mental profiles of materials that it proved very difficult Beckman Instruments executives examine mass spec-
to establish uniqueness. This is an example of a tech- trometer in 1953. Courtesy Beckman Coulter, Inc.
has been nique that comes along that is instrument-based and
chases applications.
revolutionized
Today gunshot residue is usually analyzed using a combination of scanning electron
by instrumental microscopy to visualize the particles and a technique known as energy dispersive x-ray
analysis to analyze elemental constituents. It is the combination that lets you make the
identification. But the problem of linking the residue to the shooter remains. The presence
methods.
of gunshot residue on a hand does not make that person the shooter, and that's the ques-
tion the police are interested in answering.
The identification of organic
compounds has been revolution-
ized by instrumental methods.
The methods used most often
include gas chromatography and
liquid chromatography with
mass spectrometry. Much of this
work involves identifying illicit
drugs. For example, the Chicago
lab of the Illinois State Police
Varian CP-3800 Gas chromatograph. Courtesy of Varian, Inc.
44 INSTRUMENTATION FOR A BETTER TOMORROW
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handles about 5,000 cases per month, of which more than 4,000 are drug cases. And
agents will tell you that they are getting only 1 or 2 percent of the drug traffic. The illicit
drug problem continues to dominate the lab landscape.
The workhorse instrument in the lab for the analysis of trace materials has always been the
microscope, which provides a rapid, convenient, and nondestructive method for viewing
such materials as hairs, fibers, and paint. A microscope can be used to identify and some-
times partly to individualize these materials, but caution is warranted. For example, many
forensic examiners recognize that hair samples cannot be individualized, but some of them We are
nevertheless have testified with a greater degree of confidence than was warranted. When
DNA evidence became available, these mistaken identifications became apparent. Quite a natural
few reputations of labs and examiners, whether they acted out of ignorance or because of
misguided efforts to please prosecutors, have been destroyed in the process.
beneficiaries
Today, analysis of biological evidence consists
mostly of DNA profiling. However, an essential of the
element of this profiling is the sampling and
identification steps that precede the actual analy- legacy of
sis of DNA. An important consequence of DNA
profiling has been the enablement of construct- Dr. Beckman.
ing databases of offenders. Every state in the
nation has passed legislation mandating the
databasing of DNA profiles of criminals. Some
databases include only those convicted of sexual
assaults, while others include all felony offenders,
and the trend is in the direction of databasing
more people, not fewer.
Despite relatively efficient typing or profiling
methods, databasing and casework demands
have overwhelmed many forensics laboratories.
Part of the reason is that the front-end processing of material is still very labor intensive.
It requires judgment and is difficult to automate. The federal government and the states
are working to alleviate this problem. Meanwhile, there are many opportunities for
automation and innovation to address databasing bottlenecks.
INSTRUMENTATION FOR A BETTER TOMORROW 45
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A critical issue for forensic laboratories is the admis-
sibility of forensic evidence in court. The 1992
Supreme Court case Daubert v. Merrell Dow
Pharmaceuticals addressed this concern. The case
established that scientific evidence presented in a
court has to have a solid scientific underpinning,
and it established guidelines for making this deter-
mination. Establishing the scientific underpinnings
for a particular argument can be particularly diffi-
cult for pattern evidence. Even in the case of finger-
prints, which are widely accepted as being unique,
the scientific validity of that uniqueness has never
been demonstrated. Biometric specialists are now
addressing this issue, but considerable work still
needs to be done to establish standards and tech-
niques for the use of fingerprint evidence (Figure 22).
Another example involves identifying bullets from
particular firearms. Each handgun or rifle makes
distinctive marks on the casing of a bullet, and these
marks can be observed and assessed to determine if
a bullet was fired from a particular gun. Recently, I
have been participating in experiments on consecu-
tively manufactured gun barrels to determine the
extent to which any two firearms can be distin-
guished. The marks are different, but not by much.
FIGURE 22 The sophistication of modern law enforcement
has greatly increased with the advent of new technologies.
Forensic science is by definition an applied enter-
Computer databases of fingerprints, chemical testing, and
genetic analysis are among the many advanced tools used prise, using scientific, technological, and analytical
in such investigations. methods to answer questions that are involved in
legal and regulatory matters. We are natural benefi-
ciaries of the legacy of Dr. Beckman.
46 INSTRUMENTATION FOR A BETTER TOMORROW
Representative terms from entire chapter:
forensic science
