Special Reports

San Francisco

THE FBI has found an ingenious way to catch crooks—by looking at their jeans. Scientists from the bureau reported at last week's meeting of the American Academy of Forensic Sciences in San Francisco that every pair of blue jeans has a unique wear pattern. The FBI has already used this "bar code" to place a suspect at the scene of a crime.

Richard Vorder Bruegge, a forensic scientist at the FBI laboratory in Washington DC, and his colleagues developed the technique while helping to identify suspects who were robbing banks and setting off bombs in Spokane, Washington. In April 1996, one of the gang was caught on film. He was wearing a mask, but part of his trousers was visible.

When the photograph was enlarged, Vorder Bruegge noticed light and dark lines running across the seam of the man's jeans. His team found that the pattern originated from slight imperfections introduced when the trousers were made. Workers sew the seams by pushing the fabric through a machine, and the irregularity of that motion stretches and bunches the fabric. The dyed layer of cotton in the raised portion is worn away, creating white bands.

The patches are more striking on jeans than other types of trousers because they are often allowed to become extremely worn. "People just keep wearing them," says Vorder Bruegge.

The FBI analysed the jeans of suspects in the Spokane case. One pair had a pattern with over two dozen features that matched the jeans Vorder Bruegge's team photographed. At the trial, the defence called in a used jeans exporter as an expert witness who claimed the patterns were common to all jeans. He showed the court 34 similar pairs, but in each case the FBI could distinguish them from the accused's. The suspect was convicted.