[Paleopsych] NS: Why we cannot rely on firearm forensics

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Why we cannot rely on firearm forensics
      * 23 November 2005
      * Robin Mejia

    TYRONE JONES is serving a life sentence, in part because of a
    microscopic particle that Baltimore police found on his left hand. At
    his trial for murder in 1998 the crime-lab examiner gave evidence that
    the particle was residue from a gunshot. He claimed Jones must have
    held or fired a gun shortly before his arrest.

    Jones denies this and still protests his innocence. His defence team
    is appealing the conviction, claiming that the science of gunshot
    residue (GSR) analysis is not as robust as the prosecution claims.

    Now, a New Scientist investigation has found that someone who has
    never fired a gun could be contaminated by someone who has, and that
    different criminal investigators use contradictory standards. What's
    more, particles that are supposedly unique to GSR can be produced in
    other ways.

    Forensic scientists often testify that finding certain particle types
    means the suspect handled or fired a weapon. Janine Arvizu, an
    independent lab auditor based in New Mexico, reviewed the Baltimore
    county police department's procedures relating to GSR. Her report
    concludes: "The BCPD lab routinely reported that gunshot residue
    collected from a subject's hands 'most probably' arose from proximity
    to a discharging firearm, despite the fact that comparable levels of
    gunshot residue were detected in the laboratory's contamination
    studies." The BCPD did not return calls requesting comment.

    Some specialists argue for a more cautious approach. "None of what we
    do can establish if anybody discharged a firearm," says Ronald Singer,
    former president of the American Academy of Forensic Sciences and
    chief criminalist at the Tarrant county medical examiner's office in
    Fort Worth, Texas.

    Peter De Forest of John Jay College of Criminal Justice in New York
    goes further. "I don't think it's a very valuable technique to begin
    with. It's great chemistry. It's great microscopy. The question is,
    how did [the particle] get there?"

    GSR analysis is commonly used by forensic scientists around the world.
    In Baltimore alone, it has been used in almost 1000 cases over the
    past decade. It is based on identifying combinations of heavy metals
    in microscopic particles that are formed when the primer in a
    cartridge ignites. The primer sets off the main charge, which expels
    the bullet.

    There is no standardised procedure to test for GSR, but the
    organisation ASTM International, which develops standards that
    laboratories can look to for guidance, has developed a guide for
    performing the technique that was approved in 2001. This states that
    particles made only of lead, barium and antimony, or of antimony and
    barium are "unique" to gunshot residue. The particles are identified
    using a scanning electron microscope and their composition analysed
    using energy-dispersive spectrometry.

    But recent studies have shown that a non-shooter can become
    contaminated without going near a firearm. Lubor Fojtásek and Tomás
    Kmjec at the Institute of Criminalistics in Prague, Czech Republic,
    fired test shots in a closed room and attempted to recover particles 2
    metres away from the shooter. They detected "unique" particles up to 8
    minutes after a shot was fired, suggesting that someone entering the
    scene after a shooting could have more particles on them than a
    shooter who runs away immediately (Forensic Science International, vol
    153, p 132).

    A separate study reported in 2000 by Debra Kowal and Steven Dowell at
    the Los Angeles county coroner's department reported that it was also
    possible to be contaminated by police vehicles. Of 50 samples from the
    back seats of patrol cars, they found 45 contained particles
    "consistent" with GSR and four had "highly specific" GSR particles.
    What's more, they showed that "highly specific" particles could be
    transferred from the hands of someone who had fired a gun to someone
    who had not. This doesn't surprise Arvizu. "If I was going to go out
    and look for gunshot residue, police stations are the places I'd
    look," she says.

    Scientists using the technique are aware of the potential
    contamination problem, but how they deal with it varies. In Baltimore,
    for example, the police department crime lab's protocol calls for at
    least one lead-barium-antimony particle and a few "consistent"
    particles to be found to call the sample positive for GSR. The FBI is
    more cautious. Its protocol states: "Because the possibility of
    secondary transfer exists, at least three unique particles must be
    detected...in order to report the subject/object/surface 'as having
    been in an environment of gunshot primer residue'." So a person could
    be named as a potential shooter in Baltimore, but given the benefit of
    the doubt by the FBI.

    Even worse, it is possible to pick up a so-called "unique" particle
    from an entirely different source. Industrial tools and fireworks are
    both capable of producing particles with a similar composition to GSR.
    And several studies have suggested that car mechanics are particularly
    at risk of being falsely accused, because some brake linings contain
    heavy metals and can form GSR-like particles at the temperatures
    reached during braking.

    In one recent study, Bruno Cardinetti and colleagues at the Scientific
    Investigation Unit of the Carabinieri (the Italian police force) in
    Rome found that composition alone was not enough to tell true GSR
    particles from particles formed in brake linings (Forensic Science
    International, vol 143, p 1).

    At an FBI symposium last June, GSR experts discussed ways to improve
    and standardise the tests. The bureau would not discuss the meeting,
    but special agent Ann Todd says the FBI's laboratory is preparing a
    paper for publication that "will make recommendations to the
    scientific community regarding accepting, conducting and interpreting
    GSR exams".

    Singer maintains that the technique is useful if used carefully. "I
    think it's important as part of the investigative phase," he says,
    though not necessarily to be presented in court. But he adds: "There
    are people who are going to be a bit more, shall we say, enthusiastic.
    That's where you're going to run into trouble."

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American Academy of Forensic Sciences http://www.aafs.org/

John Jay College of Criminal Justice

ASTM International

Forensic Science International

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