[Paleopsych] SW: On DNA as Evidence

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History of Forensic Medicine: On DNA as Evidence
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    The following points are made by Peter Gill (New Engl. J. Med. 2005
    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
    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
    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:
    The following points are made by Jessica Snyder Sachs (citation
    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
    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:

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