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DNA hard to challenge, but fingerprints may be attacked

DNA evidence may be tough to challenge, given the scientific rigor behind its development as a forensic tool.

But that same rigor does not support other kinds of evidence taken for granted in today’s courtrooms.

There is a dearth of peer-reviewed, published studies establishing scientific bases for the reliability of such widely accepted techniques as fingerprint and firearm identification, according to three experts who briefed a group of state public defenders on a report issued in February by a committee of the National Academy of Sciences.

Studying the country’s forensic science system, the committee found many forensic science labs are underfunded, understaffed and have no effective oversight. Too often they are extensions of law enforcement rather than truly independent, according to the report.

The report found the thoroughness of DNA research to be an exception to the lack of real science in forensic techniques.

But even though the science of DNA profiling is sound, “not all of DNA profiling is science,” said Dan Krane, professor of biological sciences at Wright State University and a member of the scientific advisory committee for the Virginia Department of Forensic Science.

Defense attorneys should not waste their time by challenging the scientific principles that produce testimony that there is only one chance in a quadrillion that material at a crime scene could have come from another person, Krane said.

In the past 20 years, the amount of DNA material needed for analysis has gone from a spot the size of a dime to a few cells invisible to the naked eye, while the length of time to conduct an analysis has been reduced from weeks or months to an afternoon and the cost of performing it has plummeted.

In fact, he said, the science has gone to the point that DNA analysis cannot only connect the blood on the blade of a knife to a victim, but DNA material on its handle from the perpetrator.

The accuracy of such determinations still depends on scrupulous procedures and methodologies from the investigators collecting the evidence and the technicians performing the tests, Krane said.

Defense attorneys should obtain field notes from the investigators and bench notes from the technicians to make sure that samples were not mislabeled or contaminated, he said.

The best procedure, adopted earlier this year by the Virginia forensics lab for DNA analysts, is for technicians to conduct “blind” tests, to make comparisons with no information about what investigators expect – or hope – they will show.

The tendency – often innocent – to conform findings to what is expected was the focus of presentations by Roger Koppl, the director of the Institute for Forensic Science Administration at Fairleigh Dickinson University and Keith Inman, assistant professor of Forensic Science at California State University, East Bay, and a senior forensic scientist at Forensic Analytical Sciences Inc.

Koppl is also a professor of economics and finance, and the focus of his forensic research is on structuring systems and organizations to reduce errors.

“Organizing forensic science under the police skews preferences and prior beliefs in favor of matches,” he said.

Inman agreed. “When you are suspect-centric rather than evidence-centric, you will make a lot of errors,” he said. “If you think it’s the guy, any difference can be explained. If you’re not looking for dissimilarities, you won’t see them.”

He noted the response of the International Association of Identification, which calls itself the world’s oldest and largest forensic organization, to the NAS report.

The association said examiners should not assert that their tests are infallible and should avoid stating conclusions in absolute terms when dealing with population estimates.


On the other hand, the association said no research projects have refuted the principle that fingerprints are unique and permanent or suggested that matches can’t be made.

Inman said the onus should be on the proponents of the accuracy of fingerprint identification to establish their reliability by scientific means rather than to point to the absence of contrary studies.

He noted, for example, that the association has adopted no standards for determining when a fingerprint left at a crime scene matches the known impressions of a suspect.

All three experts acknowledged that challenges to such underlying assumptions as the uniqueness of fingerprints will be difficult to win.

“Choose your challenge carefully,” Inman said. Even then, “Do not expect to win your first, subsequent or tenth challenge.”

David J. Johnson, executive director of the Indigent Defense Commission, said the nature of the presentation earlier this month is reflection of the state’s budget difficulties.

He would have preferred the program to be part of a conference that could be attended by all the system’s assistant public defenders, as has been the case in the past.

Instead, about 40 PDs attended the presentation, and they will take DVDs and written materials from it back to their local offices for review by the rest of their staffs.

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