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Thread: Forensics Under Fire 1
12-06-06, 09:12 AM #1
Forensics Under Fire 1
Forensics Under Fire
The unparalleled accuracy of DNA analysis has forced traditional forensic science -- long unquestioned in the courtroom -- to stand trial.
By David Dobbs
On May 30, 1997, patrolman Gregory Gallagher got out of his squad car in Boston's Roxbury neighborhood and approached a young man who was acting suspiciously. The man started running, and Gallagher chased him down an alley and over a fence. When the patrolman landed on the other side, the man grappled with him and took his handgun, opening fire as Gallagher scrambled back over the fence. One round hit Gallagher's bulletproof vest; another found flesh, hitting him in the leg. The assailant then jumped a couple of more fences into another backyard. He entered the house and demanded a glass of water from the terrified occupants.
On that glass were fingerprints that experts matched to Stephan Cowans, a Boston local who had an outstanding warrant for larceny. Gallagher identified Cowans as his assailant, as did another witness. But, it was testimony from two members of the fingerprint team that clinched the conviction: The prints, they said, unquestionably matched Cowans's.
In 2004, more than five years into Cowans's 35- to 50-year sentence, analysis of DNA left on the glass--and on a sweat shirt and baseball cap the assailant also left behind--proved Cowans to be innocent. It was hardly Boston's finest's finest hour. In fact, it was such an embarrassment for the department that the police commissioner closed the fingerprint lab for almost two years.
With fingerprints, as with other forms of traditional evidence, the conclusion rests on the expert opinion of an examiner. Though there's no rule for how many points must align, the 20 at right would be considered more than enough to call it a match. (Fingerprints by Meghan Miller/John Jay College)
The Cowans case gave Boston a whopping headache, and it generated a lasting shiver in crime labs across the country. Fingerprinting was their gold standard; never before had DNA evidence overturned a conviction based on matching prints. Now, says Lawrence Kobilinsky, professor of forensic science at the John Jay College of Justice at the City University of New York, "this is happening across the board. Whether you're talking fingerprints, tire marks or firearms, DNA has caused people to realize that these disciplines are not completely reliable."
As a result, prosecutors have begun to change their strategy in court. "Some methods you lean on less readily these days," says Astoria, Ore., District Attorney Joshua Marquis. "Hair analysis, fiber analysis, bite marks--you don't want to base too much of a case on those. Some prosecutors succumb to the temptation to rest their case on a fiber or a hair. But a good case is made up of a bunch of little things."
The new gold standard in forensic ID is the DNA match. A product of modern biological science, the DNA match was vigorously challenged when first used in court in the mid-1980s. DNA experts then did what traditional forensic ID experts never had to do: They thoroughly documented their technique. Put simply, DNA matching identifies the most distinctive genetic sequence in a sample of hair, tissue or fluid and calculates the likelihood that sequence exists in more than one person. If the sample quality is high enough, the odds can be one in trillions.
The Supreme Court shook the foundation of forensic science in Daubert v. Merrell Dow Pharmaceuticals, when it ruled in 1993 that evidence should meet standards of peer review, replicability, documentation and stated rates of probable error--all of which DNA analysis can claim. Traditional methods, in comparison, fall far short. "These techniques are not quite junk science," says Michael Saks, a law professor at Arizona State University, "but they are junky. They make claims of accuracy or even infallibility that they can't back up. The fact is," he says, "we don't know how accurate these methods are because no one's ever done extensive studies to find out."
The few small studies that have been conducted suggest that error rates run from the low single digits (for fingerprints) to the teens (hair matching) and the 60s (voice recognition). The accuracy of a match depends not just on the sample quality but on the experience, judgment and integrity of the forensic examiner.
In addition, practices may differ significantly among labs. The procedures for analyzing fingerprints, for example, vary from nation to nation, state to state and town to town. Depending on the jurisdiction, eight or 12 or 16 identical "points," or ridge endings, qualify two fingerprints as a match. Given that many crime-scene prints are only partial, discerning these points can be difficult. And while no deep data exists for error rates, fingerprint examiners often express certainty on the stand.
Of 86 convictions overturned by DNA analysis, Saks found that traditional forensic evidence had played a role in securing 54; among factors such as poor legal representation and botched police work, only eyewitness testimony was involved in more wrongful convictions (61). "These methods may help convict the guilty," Saks says, "but they also convict the innocent. We've got to stop overselling them so juries can make fair decisions."
Hair samples are examined under a comparison microscope (at right, magnified 250 times). If the hairs exhibit similar characteristics, such as structure and pigmentation, they may have come from the same person. If there are significant differences, that possibility is ruled out. Unless the hair is analyzed for DNA, a definitive match can't be made. (Photograph courtesy of Max Houck/Fundamentals of Forensic Science)
Bite-mark evidence was first used in court in 1954, and has been helping win convictions, including that of serial killer Ted Bundy, ever since. Few dispute that every person has a unique arrangement of teeth. The question is whether a bite mark reliably reflects it. Skin is elastic--it slips and moves, compresses and stretches--and bite marks change even in dead flesh. Sometimes the marks are so distinctive that identification is straightforward. More often, they appear vague or ordinary. Experts, certified as forensic odontologists, try to find similarities of general characteristics. Some analysts compare dental impressions to bite-mark photographs, or overlay computerized versions of these; more rarely, some compare 3D images of wounds, created with CT scans, to 3D images of teeth.
The most damaging challenge to bite-mark evidence involved a Phoenix cocktail waitress found stabbed to death in 1991 in the nightclub where she worked. She had been bitten twice, and the marks suggested a gap-toothed assailant. Suspicion soon centered on bar patron Ray Krone. Branded by the press as "the snaggletooth killer," he was convicted and sentenced to death. Ten years later, DNA testing of saliva on the woman's tank top was used to free Krone from death row and identify the real murderer.
Another forensic standby, firearm identification, has been used since the early 1800s. But it, too, is losing legal ground. To link a gun to a specific crime, examiners assume two things: that each firearm consistently leaves unique marks on bullets and spent casings; and that an expert can reliably match these to the weapon. In order to do this, an examiner fires rounds from a suspect's gun and places the bullets or casings under a microscope with those found at the crime scene, searching for similarities.
Simple--but complicated. Guns of the same type tend to leave similar marks, so an examiner must learn to distinguish those made by an individual weapon. In addition, bullets of different brands fired from the same gun may take on different markings. This ambiguity was argued in the courtroom in 1996 when Michael Prochilo was tried for shooting at police. A Raven .25-cal. pistol was found between the used car lot, where the shots were fired, and the place where Prochilo had stolen a vehicle. An expert testified that bullets found at the scene matched those fired from the gun. Prochilo's lawyers moved to exclude the evidence on the grounds that it didn't meet the Supreme Court's Daubert criteria. The judge allowed the testimony, but the jury found reasonable doubt. Prochilo walked.
When a gun is discharged, the cartridge is struck by a firing pin that leaves a unique impression. In order to determine if two cartridges came from the same weapon, as at right, an examiner would analyze this firing pin impression as well as the breech face markings surrounding it. In this case, the two cartridges have been deemed to come from the same semi-automatic pistol.We are the thin blue line
and all the money in the world.
And no you can't have any.
12-06-06, 09:12 AM #2
Forensics Under Fire 2
Forensics Under Fire 2
Forensic examiners seek patterns. While few would deny the legal pattern seen here, many still believe that, when performed conscientiously and rigorously, traditional forensic methods are reliable. "But we're facing a degree of skepticism we've not seen before," says Pat Wertheim, a fingerprint expert and consultant. "It's clear that we need to do more to demonstrate [these methods'] scientific basis."
Each time DNA evidence reverses a conviction, or prosecutors use Daubert to exclude evidence from a case, the pressure increases to prove the validity of a given forensic technique. This spring, the National Institute of Justice earmarked $600,000 to study the role and impact of forensic science. This research could help provide the scientific underpinnings that traditional methods now lack.
In the meantime, some forensics experts are already working to ensure more rigorous and objective analysis. Jennifer Hannaford, a fingerprint analyst with a degree in forensic science and nearly 10 years' experience in the field, was assigned to head the newly reopened Boston Police Department fingerprint lab.
Her first step was to hire four examiners who all entered forensics through academic training, and who, to promote objectivity, are employed as civilians. She plans to test the examiners for proficiency annually, standardize protocols for state-of-the-art analysis and gain accreditation from the American Society of Crime Laboratory Directors.
"In the history of a science, it is not unusual to ask new questions from time to time," says Hannaford, who views the challenges facing forensics as an opportunity to re-examine the discipline--a necessary step for progress. "We need forensics for good law enforcement," she says. "But justice requires that it be sound. If we want to convince juries that it is, we have to raise our standards."
We are the thin blue line
and all the money in the world.
And no you can't have any.
12-06-06, 09:32 AM #3Banned
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I have a question here. With the firearms testing - let's say a state requires a sample from a weapon. Will that test cross reference to different ammunition? How reliably?
There's plenty of room for commentary in this - I'll leave that to others. This is a question I've had for awhile and now seems as good a time to ask it as any. (and what better place?)
12-07-06, 01:10 AM #4
Great article. I've griped in the past about "inconclusive" lab results on handwriting, trace evidence, and toolmarks, but maybe now, I'll shut up....
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