BOSTON -- No two fingerprints are exactly alike.
For nearly a century, that widely accepted belief has been enough for police, juries and the general public to feel confident that a fingerprint match in a criminal case is all the proof needed for a conviction.
But lawyers for a man who is facing his second trial in the killing of a Boston police officer are challenging the accuracy of fingerprint analysis and asking the state's highest court to prohibit its use in criminal trials until its reliability can be proven through scientific testing.
The Supreme Judicial Court is scheduled to hear arguments Wednesday in the case of Terry Patterson, who is being retried in the 1993 killing of Boston police Detective John Mulligan.
Mulligan was shot five times in the head as he sat in his truck while on a paid security detail in the parking lot of a Walgreens drug store. The SJC overturned Patterson's conviction five years ago after ruling that his defense attorney was ineffective.
At Patterson's first trial, a police sergeant testified that four latent fingerprints found on the driver's side window of Mulligan's vehicle belonged to Patterson.
Patterson's lawyers are asking the SJC to stop prosecutors from using the fingerprint evidence at his second trial, arguing the method used to produce a fingerprint "match" is unreliable.
Charles Hope, one of Patterson's attorneys, said fingerprint experts have consciously "built up this mystique" that fingerprint identifications are infallible.
"They sort of leap from the claim that because no two fingerprints are alike, they can take a blurry, half-finished latent print from a crime scene and uniquely match that to one fingerprint," Hope said. "There's just nothing in terms of scientific study or research to back up their ability to do that."
The Patterson case is being closely watched in the legal and scientific communities. Two cases last year raised concerns about fingerprint analysis and generated extensive media coverage.
In Boston, Stephan Cowans was freed after spending six years in prison in the shooting and wounding of a Boston police officer based on a fingerprint found on a glass near the crime scene was wrongly identified as his. The Cowans case prompted the closure of the police department's fingerprint unit.
In Oregon, attorney Brandon Mayfield was arrested after FBI fingerprint experts wrongly matched his fingerprint to one of the latent prints found on a detonator bag near the train bombing in Madrid that killed 191 people.
In the Patterson case, prosecutors introduced fingerprint evidence taken from the door of Mulligan's truck -- four prints from separate fingers of the same hand. A police sergeant testified that there were enough points of comparison to identify the print as Patterson's. During cross-examination, the state's expert acknowledged that this method of identification -- adding up points of comparison from different fingers -- was not the standard method for fingerprint identification.
Patterson's attorneys, along with 15 law professors and scientists who have filed a legal brief supporting the challenge, argue that fingerprint analysis has no uniform standards for how many points of comparison constitute a match. Different law enforcement agencies have different standards, they argue, and with that comes the kind of subjective analysis that leads to errors.
In addition, fingerprint analysis has not been subjected to the kind of scientific study and testing that other forms of evidence, including DNA, have undergone, said Jennifer Mnookin, a law professor at the University of California, Los Angeles.