If you have plans to rob a bank or stick up a 7Eleven, best stick with the formal wear – slacks or corduroys – and leave the blue jeans in the closet. FBI scientists reported at the American Academy of Forensic Sciences in February that they are using a new technique to identify criminals – analyzing the unique wear patterns of denim jeans and comparing them to photographs taken from crime scenes.

Richard Vorder Bruegge, a scientist in the photographic unit at the FBI's forensics lab, developed the technique during an investigation into the bombings and bank robberies that occurred in Spokane, Washington, during the spring and summer of 1996.

At the trial, in June 1997, the criminals were convicted based in part on the FBI's analysis of their jeans. Unlike hair and fiber analysis, this technique involves no chemistry and is strictly a comparison between photographs and the articles of clothing submitted as evidence. Vorder Bruegge says it's the same sort of comparison a forensics scientist would make to match a fingerprint or tire tread, looking for unique patterns.

When FBI field agents arrest suspects, they also have a search warrant for their home and car. Vorder Bruegge said that in the Spokane case the agency gathered hundreds of articles of clothing, including 27 pairs of jeans, to look for traces of explosives.

As you continually wash jeans, Vorder Bruegge says, the dye rubs off and exposes the white cotton underneath. They fade in a unique pattern, he says, because in their manufacture, the motion of pulling the jeans through a machine causes inconsistent bumps along the seams. Primarily, the FBI looks at the fading that results from these manufacturing inconsistencies. When the bureau analyzed the jeans in the Spokane case, one pair matched more than two dozen features of the jeans in the crime scene photograph.

"The main reason we were able to make out these jeans in particular was because the bank that was robbed used high quality 35mm cameras. Unfortunately, most places today are using video cameras, which have poorer resolution," Vorder Bruegge says.

Jack King, Public Affairs Director at the National Association of Criminal Defense Lawyers (NACDL) is skeptical of the FBI's newfound fashion sense.

"Even with digitally enhanced photography, I have severe doubts about this technique, and will continue to have severe doubts until it's proven conclusively. It sounds like voodoo to me," he says.

In the Spokane case, one of the gang was caught on film in April 1996. He was wearing a mask, but part of his faded jeans was visible, and he stood still long enough for the camera to get a clear picture.

Although this was the first time the FBI was able to derive conclusive evidence from this type of seam fading, the bureau was able to place another criminal at the scene of a crime based on a circular pattern caused by a can of chewing tobacco repeatedly stored in one suspect's back pocket.

At the Spokane trial, a used-jeans exporter was an expert witness for the defense, and he claimed the patterns were common to all jeans. From a total of 400 pairs of jeans, he showed the court 34 similar pairs, but in each case the FBI could distinguish them from the accused's.

Still, the NACDL's King remains skeptical that photographic evidence is clear enough to analyze something as subtle as jean wear patterns.

"Photographic analysis is often very subjective," King says. "Unlike fingerprints, even with a good camera at a good distance, the photographs aren't necessarily that good. It's hard to make out someone's face from a surveillance camera, let alone a pattern in jeans."