82 DNA probe
A primary function of the firearms section is to deter-
mine whether a questioned bullet (for example, removed
from the body of a shooting victim) was fired from a known
(suspected) weapon. Rifling in a weapon’s barrel cuts
impressions into a bullet’s surface, but fine striations unique
to a given barrel are superimposed on these impressions.
Analysts fire the suspected weapon two or more times into
a water tank (for handguns) or a cotton waste recovery box
(for rifles), which stops the bullets without damaging them.
If the impressions and striations around the entire circum-
ference of these recovered bullets match those on the
questioned bullet (as viewed under a comparison micro-
scope), then the same weapon fired all the bullets. This
analysis is physical. But chemistry also enters into the
firearms section; one example is serial-number restoration.
Often weapons (or other metal parts such as motor-vehicle
engine blocks) arrive at the lab with their serial numbers
obliterated. Serial numbers are usually die stamped; this
process cold-works the metal in the area immediately sur-
rounding and a short distance below the penetration of the
die. The cold-worked metal is less resistant to chemical
attack than the base metal. Polishing the obliterated area,
then etching the area with a chemical suitable for the par-
ticular metal (sometimes with an applied voltage to speed
up the attack), can make the numbers visible again. Serial-
number restoration also works with plastic parts; cold-
worked plastic is less heat-resistant than the base plastic,
so one can replace etching with a high-intensity lamp.
The drug-chemistry section analyzes evidence believed
to contain illegal or controlled substances. Evidence is most
often tablets, capsules, powder, crystals, or vegetation. Scien-
tists isolate the active ingredient(s) using solvent extraction
and then perform several chemical tests. Final identification is
accomplished by one or more techniques considered to pro-
duce a “chemical fingerprint” for a substance: infrared (IR)
spectroscopy, nuclear magnetic resonance (NMR) spec-
troscopy, or mass spectrometry (MS). Rarely is the mass
spectrometer used alone; it is linked instead to either a gas
chromatograph or a liquid chromatograph, hence the names
GC-MS and LC-MS, respectively. The hyphenated techniques
are especially useful if solvent extraction yields a mixture
rather than one pure compound. The chromatograph sepa-
rates the mixture; one by one, each compound is identified as
it passes into the mass spectrometer.
The author is assigned to the toxicology section, which
will provide the final examples of chemical analysis. Toxicol-ogists analyze body fluids (such as blood and urine) and
body tissues (such as liver, brain, and stomach contents,
although the last item is not strictly a tissue) for the pres-
ence of (and often the amount of) drugs and poisons. These
items are submitted in two main types of cases. The first is in
arrests of motorists for driving under the influence of alcohol
and/or drugs. The second is in unattended deaths, where a
drug or poison overdose might be the cause of death. Occa-
sionally, nonbiological specimens will be submitted. One
example is suspected alcoholic beverages in cases involv-
ing violations of open-container laws (open-container laws
prohibit the possession of any open alcoholic beverage con-
tainer and the consumption of any alcoholic beverage in the
passenger area of a motor vehicle). Toxicologists isolate
drugs, poisons, and their by-products (metabolites) from
blood, urine, and tissue specimens using solvent extraction
or solid-phase extraction. A complex mixture normally
results; indentification by IR or NMR is impossible, since
these techniques require a pure substance. Hence GC-MS
and LC-MS are employed.
Toxicology can reveal the unnatural nature of what
might at first appear to be a natural death. For example, a
murderer might attempt to conceal the crime by setting a fire.
But a fire victim normally has a high blood carbon monoxide
level. A murder victim, dead before the fire began, couldn’t
inhale any carbon monoxide. In another example, the author
analyzed autopsy specimens from a 43-year-old female found
dead in bed. Lethal levels of chloroform (an industrial solvent)
were found. When confronted by this evidence, the woman’s
estranged husband admitted entering the house while she
slept and covering her mouth and nose with a chloroform-
soaked tissue.
Other times a death really is natural. The author ana-
lyzed autopsy specimens from Sergei Grinkov, the Olympic
pairs figure skating champion who collapsed and died dur-
ing a practice session in Lake Placid, New York. Only lido-
caine and atropine (given during resuscitation attempts)
were found.
Occasionally the toxicology section analyzes unusual
items. The author examined both fighters’ boxing gloves for
foreign substances after the 1996 Madison Square Garden
heavyweight bout in which Evander Holyfield defeated
Bobby Czyz—and found none. Czyz’s camp argued that he
could not continue because his eyes were burned from a
foreign substance on Holyfield’s gloves.—Harry K. Garberis a forensic scientist in
the toxicology section of the New York State
Police Forensic Investigation Center in
Albany, New York.What a Crime Lab Does, It Does
with Chemistry
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