Fifty people were killed and 53 more were wounded when a gunman launched an assault on a gay nightclub in Orlando early Sunday.
The shooter, identified by several law enforcement sources as Omar Mateen, 29, was killed in a shootout with law enforcement after a three-hour siege.
The massacre — the worst mass shooting in the history of the United States — began when the gunman stormed the Pulse Nightclub about 2 a.m. ET with an AR-15 type rifle and a handgun, officials said.
Among the latest developments:
- Mateen called 911 before the attack, expressing fealty to ISIS, but authorities say there's no evidence he had been in contact with any terror cells abroad or in the United States.
- The names of the first victims identified in the shooting include men between the ages of 20 and 36 years old.
- President Obama called the attack "an act of terror and hate."
- Mateen had security and firearm licenses and the gunman's weapons were legally purchased within the past week.
The carnage ended at about 5 a.m. ET, when 11 Orlando police officers and three Orange County sheriff's deputies stormed the nightclub and exchanged fire with Mateen, authorities said. City officials said about 300 people were in the club at the time of the shooting.
FBI evidence specialists arrived Sunday night at Mateen's home in a condominium that had been cleared shortly after dawn, authorities told NBC News. They were operating with great care in case the apartment might be booby-trapped but authorities said late Sunday that no devices were found, and residents were allowed back home about midnight.
Seddique Mir Mateen, Mateen's father, told NBC News that "this has nothing to do with religion" in spite of reports that his son had declared his allegiance to ISIS.
A law enforcement official told NBC News there is no indication that Omar Mateen was in touch with terrorists overseas and nothing to indicate this was a directed attack. Also, several officials say, there's no sign that anyone else was involved in the attack, either in helping Mateen or egging him on.
The father said his son got angry when he saw two men kissing in Miami a couple of months ago and thought that might be related to the shooting.
"We are saying we are apologizing for the whole incident. We weren't aware of any action he is taking. We are in shock, like the whole country," Seddique Mir Mateen said.
Law enforcement sources told NBC News that Omar Mateen was born in New York in 1986 and was listed as living in Fort Pierce, about 125 miles south of Orlando on Florida's Atlantic coast. Mateen had active security officer and firearm licenses, according to Florida records, and his family said he worked in security.
The FBI first looked into Mateen in 2013 because of a statement he had made about radical Islamic propaganda, law enforcement officials told NBC News. Ron Hopper, an assistant FBI special agent in charge of Orlando operations, said the investigation began after Mateen made offensive comments to co-workers. He was interviewed twice, but the investigation was closed after the FBI wasn't able to confirm that he had ties to radical Islam, Hopper said.
The FBI interviewed him again in 2014 when it learned that he might have a connection to a U.S. suicide bomber, but the investigation was closed because the FBI determined that "contact was minimal and did not constitute a substantive relationship," Hopper said.
Law enforcement officials told NBC News that Mateen swore allegiance to the leader of ISIS in a 911 phone call shortly before the shooting, in which he also mentioned the Boston Marathon bombers, Dzhokhar Tsarnaev and Tamerlan Tsarnaev.
Mateen legally bought the two guns used in the shooting in the past week, said Trevor Velinor, an assistant special agent in charge of the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives in Tampa.
Marriage records show he was married in Port St. Lucie in 2009, and his family said he had a 3-year-old son.
Police said that Mateen was a U.S. citizen but some of his family members aren't. They wouldn't say where those family members were from.
Meanwhile, a man who answered the phone at Mateen's address, Mustafa Abasin, told NBC News: "We are in shock, and we are sad." He wouldn't say how he knew Mateen, but he said he was helping investigators.
Rep. Alan Grayson, D-Florida, whose district includes the area of the massacre, said the attack was "more likely than not ideologically motivated."
"It's no coincidence that the attack took place where it did and when it did," Grayson said. "It might be that we've seen the commission of an awful hate crime."
Grayson said investigators were searching Mateen's home and combing the nightclub. Processing the gruesome scene would "take hours," Grayson said, adding: "There is blood everywhere."