[Paleopsych] SW: On DNA as Evidence
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History of Forensic Medicine: On DNA as Evidence
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http://scienceweek.com/2005/sw050826-6.htm
The following points are made by Peter Gill (New Engl. J. Med. 2005
352:2669):
1) In 1983, in a village near Leicester, England, a local girl named
Lynda Mann was found raped and murdered. Three years later, a second
girl, Dawn Ashworth, was found dead under similar circumstances. The
similarities between the two cases led the police to believe that the
same person had committed both crimes. After extensive inquiries, an
arrest was made. The suspect confessed to the murder of Lynda Mann but
denied having killed Dawn Ashworth. Convinced that they had the right
man, the police approached Sir Alec Jeffreys, a professor of genetics
at the University of Leicester, with a request to conduct tests using
a new method that he called "DNA fingerprinting," which had not yet
been used in a real case.
2) The results were surprising: the suspect was exonerated, and the
DNA profiles in the two murder cases were the same, indicating that a
single, unknown person had committed both crimes. This finding led to
the screening of all 5000 men in the area, using both conventional
blood-group methods and DNA testing. The screening failed to identify
a suspect -- because, as it turned out, the perpetrator, Colin
Pitchfork, had paid a colleague to give a DNA sample in his place.
When the colleague was overheard bragging to a friend about the
incident, Pitchfork was quickly apprehended, analysis of a DNA sample
confirmed his guilt in both murders, and he was duly convicted in
1988.[1]
3) Thus, the first criminal case in which DNA was used provided a
vivid demonstration of the method's potential -- not only for
convicting the guilty but also for exonerating the innocent. It also
demonstrated for the first time that a DNA fingerprint could be used
to find a perpetrator from within a population.
4) In 1985, a year after the development of DNA fingerprinting, the
polymerase chain reaction (PCR) was discovered.[2] The discovery would
revolutionize the field of molecular biology, though the method would
not come into routine use in forensic cases until the early 1990s,
since new platforms and biochemical tools were needed in order to take
full advantage of the potential of PCR. In particular, new automation
technology was key, and the advent of the automated fluorescent DNA
sequencer in the early 1990s was a major step forward. More generally,
forensic DNA analysis has benefited substantially from the Human
Genome Project, for the genome could be sequenced only with automated
equipment that permitted high-throughput processing. Because forensic
science could use the same equipment and biochemical tools that gene
sequencing used, new methods were rapidly developed in the early 1990s
that would have been considered impossible just a few years earlier.
5) Perhaps the best example of this adjunct benefit of genomics was
the development of national DNA databases. Since its inception in
1995, the National DNA Database for England and Wales has expanded to
include more than 2.75 million reference DNA profiles, against which
all specimens obtained from the scene of a crime ("crime stains") are
routinely compared.[3] The likelihood that a match will be found is
approximately 30 percent. Many other countries have since followed
suit, and the benefits of such databases are considerable, since
persons who commit serious crimes such as murder usually have a
previous criminal record. The United Kingdom's policy permits the
collection of DNA profiles from all convicted criminals, as well as
from anyone suspected of committing a crime that could lead to a
prison sentence -- and the law allows authorities to retain the DNA
profile even if the suspect is found innocent. Consequently, persons
who later commit more crimes can be identified and apprehended
quickly.[3-5]
References:
1. Wambaugh J. The blooding. London: Bantam Press, 1989
2. Saiki RK, Scharf S, Faloona F, et al. Enzymatic amplification of
beta-globin genomic sequences and restriction site analysis for
diagnosis of sickle cell anemia. Science 1985;230:1350-1354
3. Werrett D, Pinchin R, Hale R. Problem solving: DNA data acquisition
and analysis. Prof DNA 1998;2:1-6
4. Gill P, Whitaker J, Flaxman C, Brown N, Buckleton J. An
investigation of the rigor of interpretation rules for STRs derived
from less than 100 pg of DNA. Forensic Sci Int 2000;112:17-40
5. Marchi E. Methods developed to identify victims of the World Trade
Center disaster. Am Lab 2004;36:30-36
New Engl. J. Med. http://www.nejm.org
--------------------------------
Related Material:
ON THE NATURAL SCIENCES AND FORENSICS
The following points are made by Jessica Snyder Sachs (citation
below):
1) Anthropologists were the first to cross over from the natural
sciences to forensics. In America, the fateful jump came in the 1930s,
when FBI agents setting up the bureau's first crime lab in Washington,
D.C. discovered a whole nest of "bone detectives" in the red Gothic
towers of the Smithsonian Institution, across the street. As the
curators of one of the world's largest collection of human skeletons,
the Smithsonian anthropologists were uniquely qualified to help the
FBI distinguish human from animal remains. From the identification of
bones as human, forensic anthropology quickly advanced to the
identification of individuals, based on distinguishing bumps and bony
scars left by past injuries and the wear and tear of daily toil (a
milkmaid's worn elbow, a tailor's notched thumb, and a mailbag
carrier's crooked spine).
2) But anthropologists quickly realized the near-impossibility of
naming the dead without some method, however crude, of matching their
identity clues to missing person reports for a given span of time. The
most experienced among them could sometimes come up with a reasonable
estimate of time since death by "feel" -- that admittedly
nonscientific second sense based on a lifetime of processing decayed
corpses and crumbling bones. But precious few ever attempted the
monumental task of objectively studying the stages that mark a human
body's passage back to dust. So far, the most valuable dating method
to come out of their research belongs by all rights to another
science.
3) In the i980s, the field of forensic entomology burst on the scene
as if out of nowhere when bug and bone scientists independently
discovered the value of what may be nature's ultimate postmortem clock
-- the cadaver-feeding insect. Maggots, once routinely washed from the
coroner's table with disgust, suddenly became the hot new thing in
homicide investigation. Still, the extent of the bugs' testimony had
yet to be fully fathomed.
4) As anthropologists and entomologists began teaming up in their
forensic investigations, they naturally turned to a third specialty to
make sense of the roots and vines winding through their death scenes:
A delicate green tendril snaking through a sun-bleached skull. A tree
growing down through a shallow grave in the woods. A flush of growth
marking the outlines of an inexplicably fertile corner of an abandoned
lot. Each became yet another promising measure of the seasons that
follow "death most foul."
Adapted from: Jessica Snyder Sachs: Corpse: Nature, Forensics, and the
Struggle to Pinpoint Time of Death. Perseus Publishing 2001, p.9. More
information at:
http://www.amazon.com/exec/obidos/ASIN/0738207713/scienceweek
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