ORLANDO, Fla. – After a Facebook post began circulating claiming there were multiple shooters inside Pulse nightclub during Sunday's massacre, Orlando police posted a tweet to silence the rumor.
"Alert: Rumors of multiple shooters are unfounded. The one shooter, Omar Mateen, is dead. #OrlandoUnited," the tweet read.
Alert: Rumors of multiple shooters are unfounded. The one shooter, Omar Mateen, is dead #OrlandoUnited— Orlando Police (@OrlandoPolice) June 13, 2016
Mateen, who killed 49 people in the popular gay nightclub and wound more than 50 others, pledged allegiance to ISIS and mentioned the Boston Marathon bombing in a 911 call, according to a U.S. official.
Mateen, who was shot and killed in a gun battle with police, made the call more than 20 minutes into the attack, a law enforcement official said.
Mateen, who is from Fort Pierce, was armed with a handgun, an assault rifle and an unknown number of rounds, Orlando Police Chief John Mina told reporters.
The gunbattle that killed Mateen began after the gunman emerged through a hole that a police armored vehicle had made in the building to rescue hostages, Mina told reporters Monday.
"The suspect came out of that hole himself ... and engaged in a gunbattle with officers, where he was ultimately killed," Mina said.
Before that, police crisis negotiators tried to negotiate with Mateen during the attack, Mina said.
"He was cool and calm when he was making those phone calls to us," Mina said. "We had a team of crisis negotiators that did talk to the suspect just trying to get as much information as possible. ... He really wasn't asking for a whole lot. We were doing most of the asking."
FBI had investigated him twice
Born in New York to parents originally from Afghanistan, Omar Mir Seddique Mateen lived in a condo in Fort Pierce, Florida, and was a security officer at G4S Secure Solutions, one of the world's largest private security companies.
According to a neighbor, he was a security guard at the courthouse in Port St. Lucie, Florida, often manning the metal detectors at the front of the building.
Mateen was married to a woman named Noor Salman who lived with him at the condo, according to documents CNN obtained. He also had a son, 3½, according to Mateen's father.
About 20 minutes into the attack on the nightclub, Mateen called 911 and told a dispatcher he pledged allegiance to ISIS as well as mentioned the 2013 Boston Marathon bombers, a U.S. official said.
The FBI interviewed him in two terror-related cases in recent years, but both of them were closed, and he was not under investigation or surveillance at the time of the attack, Assistant Special Agent in Charge Ronald Hopper told reporters Sunday.
"Those interviews turned out to be inconclusive," Hopper said, "so there was nothing to keep the investigation going."
Mateen first came on the FBI's radar in 2013 when he made "inflammatory comments to co-workers alleging possible terrorist ties," Hopper said. But investigators "were unable to verify the substance of his comments," he said.
In 2014, the FBI interviewed Mateen again over possible connections with an American suicide bomber.
"We determined that contact was minimal and did not constitute a substantive relationship or threat at that time," Hopper said.
A message posted on a site associated with the ISIS news agency Amaq described Mateen as "an Islamic State fighter." But the language is inconsistent with previous ISIS announcements, and there was no claim the attack was directed, just an after-the-fact assertion the gunman was an ISIS fighter.
Officials stressed the investigation is in the early stages. They say they're looking into the possibility Mateen radicalized on his own.
Ex-wife: He abused me
Mateen's ex-wife, Sitora Yusufiy, painted a damning portrait of the killer, describing a physically abusive marriage to a "bipolar" man with anger issues that required her family's help to escape.
At a press conference Sunday in Boulder, Colorado, Yusufiy said the relationship had started well initially after they met online about seven years ago.
"In the beginning he was a normal being that cared about family, loved to joke, loved to have fun, but then a few months after we were married I saw his instability," she said.
"I saw that he was bipolar, and he would get mad out of nowhere. That's when I started worrying about my safety."
She said the abuse became a regular occurrence.
"He started abusing me physically, very often, and not allowing me to speak to my family, keeping me hostage from them," Yusufiy said.
"(My family) had to pull me out of his arms and find an emergency flight. ... I made a police report."
Father baffled by killings
Mateen's father, Seddique Mateen of Port St. Lucie, said he was "really puzzled" by his son's actions.
"In the United States I gave him the best education possible," he told WOFL-TV in Orlando.
"We provided for him love and care. The best possible way a father and a mother can provide. So what had happened, it's really surprised me."
The killer was known to be a semi-regular worshipper at the Fort Pierce Islamic Center.
But his father -- who had an occasional television show on an Afghan satellite channel in which he regularly criticized Afghanistan's government and Pakistan -- said he saw no religious motivation in the killing.
"Radicalism? No. He doesn't have a beard even. When someone becomes radical, they grow long beards and they wear clothes that you know, long clothes, and I don't think religion or Islam had nothing to do with this," he said.
He may have pledged allegiance to ISIS during his 911 call because "he wanted to boost himself," he said.
However, he acknowledged an incident where his son had a strong reaction to a gay couple displaying affection in Miami.
"A couple, they were touching each other in front of the kids and in front of the public. And that, he was surprised about that," he told WOFL.
Gilroy, Mateen's former co-worker at PGA Village in Port St. Lucie, said Mateen often made homophobic, sexist and racist remarks.
"He would hit things and as he was hitting things, he would yell, and of course there was always curse words involved, and this wasn't seldom, this was all the time."
He said he asked his employers not to be assigned to work alongside Mateen, but this request was denied. At that point, Gilroy told Mateen he didn't want to continue their relationship on a personal level, according to WPTV.
"He acted very negatively toward that. He then started to text me 20 to 30 times a day. Call me 15 to 20 times," he said.
He said he wished he could have done something to prevent the tragedy, the worst terror attack in the United States since September 11, 2001.
"I saw it coming. I mean everything," he said. "He said he was going to kill a whole bunch of people."