Brandon Mayfield, an American-born Portland lawyer and convert to Islam, has just been released and exonerated after having been held for about two weeks as a material witness under provisions of the Patriot Act. The basis for his arrest was a fingerprint match, which turned out to be erroneous, connecting him with the big recent bombing in Spain.
People who say that worries about the Patriot Act are exaggerated should look at this case. Mayfield was released only because Spanish police working on the case (who had doubted the FBI identification from the start) finally connected the fingerprint to a different man. Otherwise the guy would probably be in jail indefinitely.
The FBI found several fingerprint matches (perhaps by setting their computers to pull in as many matches as possible: my guess) and then zeroed in on Mayfield after they found that he was a Muslim convert who had represented a convicted terrorist in a non-political case. At first they represented the match as much closer than it really was, even though the Spanish police had their doubts.