Orlando mourns as possible motives emerge for club gunman

Amy Semesco, left, wipes a tear, while visiting a makeshift memorial for the victims of a mass shooting at the Pulse nightclub with Bree Balchunas on Tuesday, June 14, 2016, in Orlando, Fla. (AP Photo/David Goldman) (The Associated Press)

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Rhonda Rodeffer, left, and her daughter Kennedy, 4, visit a makeshift memorial for the victims of a mass shooting at the Pulse nightclub Tuesday, June 14, 2016, in Orlando, Fla. (AP Photo/David Goldman) (The Associated Press)

Amy Semesco wipes a tear as she pays tribute, Tuesday, June 14, 2016, in Orlando, Fla., at a growing memorial at the The Dr. Phillips Center for the victims of the mass shooting Sunday at the Pulse Nightclub. (AP Photo/Alan Diaz) (The Associated Press)

ORLANDO, Fla. – Thousands in Orlando are mourning 49 people killed inside a gay nightclub as federal investigators examine 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.

Meanwhile, Mateen's ex-wife says he suffered from mental illness. And his Afghan-immigrant father says his son got angry recently about seeing two men kiss.

Meanwhile, thousands gathered Monday night in downtown Orlando for a vigil to support victims and survivors of the Pulse nightclub shooting on the lawn of Orlando's main performing arts venue.