Less than three weeks after the CIA and FBI received fragmentary information from a captured senior al Qaeda operative about two men interested in exploding a "dirty" radioactive bomb in the United States, a worldwide investigation tracked down and arrested Abdullah al Muhajir, 31, according to senior administration officials. The second man, described as a Pakistani but otherwise not identified by authorities, was discovered to have already been in custody of Pakistani police for travel document violations, one administration source said. "Give me a 'P'! Give me an 'R'! Give me some good PR!" | 
