Omar Mateen, 29, walked into a gay nightclub in Orlando, Fla., Sunday morning and opened fire, according to law enforcement. He was killed after a long standoff with police but not before he allegedly carried out the deadliest mass shooting in United States history.
We will no doubt learn much more about Mateen in the coming days. But here is what we know so far:
-- Mateen, 29, was born in New York in 1986.
-- The FBI's Ronald Hopper said Mateen first drew their attention in 2013, when he made "inflammatory comments" to co-workers about having ties to terrorism.
"In the course of the investigation, Mateen was interviewed twice," Hopper said. "Ultimately we were unable to verify the substance of his comments and the investigation was closed."
-- Hopper added that the FBI investigated Mateen yet again in 2014 when he was linked to Moner Mohammad Abu-Salha, a U.S. citizen who who blew himself up that year in a suicide attack in Syria.
After investigating a second time, the FBI concluded that Mateen was not a threat.
-- According to public records, Mateen has had a firearm license since September 2011. He was also licensed to be a security officer.
-- In a statement, the global security company G4S said that Mateen had been an employee since Sept. 10, 2007.
G4S provides security in many places, including Afghanistan and Iraq.
-- Hopper said that Mateen legally bought two weapons — a hand gun and a long gun — in the past several days.
-- Hopper said Mateen called 911 right before the shooting spree to pledge his allegiance to the Islamic State.
-- Mateen's father, Meddique Mir Mateen, told NBC News, that "this has nothing to do with religion." A couple of months ago, the father told the network, Mateen was angered when he saw two men kissing.
-- Public records show that Mateen was married in 2009. The Washington Post spoke to a woman whom they identified as his ex-wife. She described Mateen as unstable.
"He beat me," she told the newspaper. "He would just come home and start beating me up because the laundry wasn't finished or something like that."
Public records show that Mateen and his wife were divorced in July 2011.
-- In a press conference in Boulder, Colo., on Sunday night, Mateen's ex-wife described her former husband as "mentally ill" and "disturbed."
She reiterated that he had been physically abusive, and thanked her family for rescuing her from the violent relationship.
She said he wanted to be a police officer, and was a licensed gun owner while they were married.
-- NPR member station WNYC reports that Mateen's parents moved to New York from Afghanistan in the 1980s. One neighbor, who spoke on condition that the station did not use his name, said the family was devoted to their children.
"[Mateen] could've been maybe 4 when he was here," the neighbor said. "[They] didn't have enough money to buy the food so the children were getting hungry."