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Testing, Testing

Local Matters


Published March 30, 2005 at 5:00 p.m.

Burlington police spent two weeks tracking Laura Winterbottom's murderer. They found him, ultimately, in a laboratory.

When authorities arrested an Old North End resident last week and accused him of murdering and sexually assaulting 31-year-old Winterbottom, it was DNA evidence that connected him to the crimes. Police said bodily fluids recovered from Winterbottom's car and body matched a sample taken from 33-year-old Gerald Tyrone Montgomery, a previously convicted sex offender. Montgomery has pleaded not guilty to both charges.

As a result of TV crime shows and highly publicized celebrity trials, most people these days have a basic understanding of DNA evidence -- what it is and how it's used in criminal cases. But a visit to Vermont's state forensic lab proves that the DNA testing process is more complicated than it looks on TV.

The state's only forensic crime lab is located behind a metal door on the third floor of the Department of Public Safety building in the Waterbury state offices complex. White walls and a gleaming tile floor give the lab an antiseptic appearance, accentuated by the strip of sticky paper that serves as a welcome mat to the DNA analysis room. Lab director Eric Buel explains that the paper helps to reduce the amount of dust in the tight space.

When police collect a sample from a crime scene, he says, they take it first to the serology department, where technicians determine, for example, if stains on a shirt are blood or chocolate sauce. If the sample contains DNA, it's liquefied and brought to the analysis room. Technicians there use pen-like injectors called pipettes to transfer the DNA-filled fluid to clear plastic tubes half an inch long and an eighth of an inch in diameter.

They run the samples through three machines. The first instrument, a "Real-time PCR," determines if there's enough DNA in the sample to test. The second, a thermocycler, replicates the DNA strands, and embeds fluorescent dyes that will enable the third machine -- the genetic analyzer -- to prepare a profile.

It's a lengthy process. "DNA analysis, unlike on 'CSI,' takes time," says Buel. As he displays the machinery, Joseph Abraham, a forensic chemist, runs a sample through the genetic analyzer. Unlike the genetic analyzer on "CSI," Abraham's machine doesn't have lights that illuminate the samples.

Inside the analyzer, a tube extends into the DNA sample, and sucks up fluid into another tube the width of a human hair. Lasers penetrate the tube to search for fluorescent dyes. Abraham stands in front of a computer linked to the machine, which interprets the data and produces a multicolored graph that is indecipherable to non-experts.

Under the best circumstances, Abraham says, the lab can produce a profile in three days. But Buel says that may extend to a week; he declines to discuss the timetable in the Winterbottom case. Homicides are obviously the first priority, but if the machine is mid-analysis, it has to finish before the next sample can be introduced.

And Buel notes that the genetic analyzer is sometimes temperamental. "If the instrument breaks and we have to call a service rep," he says, "they're out of Boston."

Once the profile emerges from the analyzer, a technician determines whether it contains enough information to deliver an accurate match. A second analyst double-checks the report. Then the profile is checked against the genetic profiles of identified suspects, and against the Vermont's Combined DNA Index database. If a match is found, technicians test the original sample to be sure they got an accurate reading. They'll take another sample once the suspect is in custody, from a cheek swab or a blood draw.

Buel says there are multiple checks built into the system. That's crucial, because the likelihood of a false match is slim. "We give statistics in the billions and trillions," he says. "Statistically, it's terrific evidence."