ORLANDO, Fla. -- As thousands in Orlando turned out to mourn 49 people killed inside a gay nightclub, federal investigators examined possible motives for the gunman who committed the worst mass shooting in modern U.S. history.
The White House and the FBI said 29-year-old Omar Mateen, an American-born Muslim, appears to be a "homegrown extremist" who had touted support not just for the Islamic State, but other radical groups that are its enemies.