• Crime lab stays on the 9/11 case

    Don Emmert / AFP - Getty Images

    Veronique Bourdon conducts research in the teaching facility at the New York City Medical Examiner's Office. Researchers are continuing to identify the remains of victims from the 2001 terror attacks. Forty-one percent of the 2,753 World Trade Center victims have not yet been matched with remains.

    By Alan Boyle, Science Editor, NBC News

    Forensic scientists are continuing to identify remains from 9/11 victims, and they could still be working on the case 10 years from now. Ten years after the terror attacks, thousands of bits of bone found where the World Trade Center's twin towers fell are unidentified, and 1,124 of the 2,753 known victims have not yet been matched up with any remains.

    Mark Desire, who heads up the identification effort for the New York City Medical Examiner's Office, notes that the crime lab handles about 500 homicides and 2,000 sexual-assault cases a year, and thousands of other investigations. But the 9/11 case is special.

    "As a forensic scientist, you're taught not to get emotionally involved," he told me today. "But the World Trade Center ... that's the exception."

    This weekend, he and his colleagues will be meeting with the families of the victims, going over everything that's been accomplished over the past year and everything they hope to do over the next year. It's what he's done on every anniversary since the attacks.

    Here are the highlights from this year's report:

    • Five scientists in Desire's office are working full-time on World Trade Center victim identification, and the effort can draw upon the 180 other employees at the medical examiner's lab.
    • More than 21,000 pieces of human remains have been collected so far, with about 13,000 of those fragments matched up to DNA extracted from samples of the victims provided by loved ones. The reference samples may come from hair in combs or hairbrushes, from flecks of skin left behind in old toothbrushes, on clothes or on jewelry, from medical samples, even from baby teeth found in photo albums. "We've become really good at disposable razors — breaking them open and taking the DNA," Desire said.
    • About 6,000 of those remains have been analyzed more than once, sometimes five or six times, as new DNA extraction techniques become available. In the old days, the scientists used to grind bone by hand to get at the DNA. Now, the lab uses liquid-nitrogen freezing, sonication and high-tech detergents to get the DNA out of bone tissue that is typically degraded by fire, water and exposure to the elements. "We need every possible cell in what's left to have any hope of generating a profile," Desire said. In the past five years, the new techniques have sparked a new wave of victim identifications.
    • The scientists analyze the DNA by looking for matching sequences known as short tandem repeats, or STRs. They can also draw upon other types of DNA tests that focus on mitochondrial DNA or single nucleotide polymorphisms (SNPs, or "snips"). If there's a full-profile match, the chances of making a wrong identification are less than 1 in a trillion. In the past, the forensics team has used dental records, other medical records and even tattoos to match remains with victims — but today, DNA is the gold standard. "We would never release remains unless we were absolutely positive that this was the individual identified, and DNA allows us to do that," Desire said.
    • About 400 bone fragments are checked every month. If there's a DNA match, it's almost always matched to a victim who has already been associated with other remains. But every six months or so, there's a new identification. The last time that happened was in August: Ernest James, a 40-year-old New Yorker who worked at the insurance firm Marsh & McLennan in the trade center's north tower, was lost on 9/11 but was finally linked to a bit of bone, thanks to the DNA.

    Desire said the thousands of yet-to-be-identified samples will continue to be stored for future analysis as new techniques are developed. He and his colleagues are already talking with the planners for the National September 11 Memorial and Museum, to make sure that unidentified 9/11 remains will stay accessible even after they're interred at the memorial.

    "They're stored now in a very low-humidity condition, preserved for years to come to be able to work with," Desire said. "They're going to be stored at the memorial in the same way."

    Every time DNA technology improves, forensic scientists will go back to those samples and check them again, hoping to give a little more closure to the thousands of families who are still wondering about their loved ones. That means that as painful as it may be, Desire and his fellow forensic scientists will be going to the anniversary gatherings with 9/11 families for years to come.

    "It is a very emotional time for all of us," Desire said. "We want to emphasize that we are there."

    More about the 9/11 anniversary:

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