ETROIT, Aug. 29 — For nearly a year, the three foreigners picked up at an apartment here a week after the Sept. 11 attacks seemed like just another group of Arab men caught up in the government dragnet. They languished in prison while facing charges that seemed minor; federal agents had actually been looking for the previous occupant when they raided the apartment.But at least one thing appears to have separated the Detroit trio from hundreds of other Arabs swept up by the government in the last year: a cooperative witness. A fourth Arab man who once lived with...