Source: "It is no coincidence that this happened in Orlando"

The gunman who murdered 49 people in a Florida nightclub early Sunday morning was a follower of a controversial gang leader-turned-bank robber who was released from prison last year despite warnings from prosecutors that he would recruit people to carry out violent acts, sources told FoxNews.com.

Omar Mateen, whose bloody siege inside a packed Orlando gay nightclub ended when SWAT teams stormed the building and killed him, was a radical Muslim who followed Marcus Dwayne Robertson, a law enforcement source said.

"It is no coincidence that this happened in Orlando," said a law enforcement source familiar with Robertson's history of recruiting terrorists and inciting violence. "Mateen was enrolled in [Robertson's online] Fundamental Islamic Knowledge Seminary."

Robertson and several associates were rounded up for questioning early Sunday, according to law enforcement sources, a development his attorney refused to confirm or deny.

Click here for some of the extensive reporting on Robertson from Fox News.