Last Updated Jun 12, 2016 10:22 PM EDT
ORLANDO, Fla. -- The gunman behind a mass shooting at an Orlando nightclub has been identified as Port St. Lucie resident Omar Mateen, CBS News confirms.
Officials are still investigating the exact motives for the shooting, and both ties to radical Islam as well as a general hate crime motivation are being considered.
The shooting and hostage situation early Sunday morning at Pulse -- which describes itself as "Orlando's hottest gay bar" -- left at least 50 people dead, including the gunman, and more than 50 injured, officials say.
A picture of the gunman has begun to surface. CBS News has confirmed that Mateen, 29, was a U.S. citizen and has Afghan parents. He was born in New York, according to the FBI. What we know about him so far:
Mateen claimed allegiance to ISIS
Sources tell CBS News correspondent Jeff Pegues that Mateen called 911 and pledged allegiance to ISIS. During the 911 call, Mateen referenced Boston marathon bombers Dzhokhar and Tamerlan Tsarnaev, Pegues reports.
Mateen called 911 from the club's bathroom, a U.S. intelligence source tells CBS News' Len Tepper. Dispatchers called him back, and Mateen then pledged allegiance to ISIS and ISIS leader Abu Bakr al-Baghdadi, Tepper reports.
Mateen gave his full name to 911 dispatchers, according to Pegues.
ISIS officially took credit for the attack on social media, but American investigators have yet to corroborate the claim. ISIS has in the past taken credit for attacks that were not planned by them.
A U.S. intelligence source told CBS News senior investigative producer Pat Milton that Islamic terrorism is being investigated as a possible motive in the shooting because of several indicators, including the style of the attack, which had similarities to the attacks in Paris in November 2015 and Brussels in March.
He was known to the FBI
Mateen had been on federal law enforcement radar in recent years. According to FBI Agent Ron Hopper, Mateen first came to the FBI's attention in 2013 when he made inflammatory comments to co-workers alleging possible ties to terrorism. He told co-workers and others he knew the Tsarnaev brothers, a U.S. intelligence source tells Tepper.
Hopper says the claims were "thoroughly investigated" and Mateen was interviewed twice. But officials couldn't verify the substance of the comments, and the investigation was closed.
Mateen again surfaced on federal radar in 2014, Hopper said, as someone who may have had ties to a suicide bomber. Mateen was again interviewed, but investigators determined the contact was minimal and didn't constitute a threat. That investigation was also closed out, Hopper said.
Mateen was not on a current terror watchlist, a U.S. intelligence source tells Tepper. He was entered into a terrorist screening database during the time the FBI was questioning him, but he was removed when the FBI closed the investigation, Tepper reports.
He legally purchased two weapons
An ATF official said Mateen had legally purchased a handgun and a "long gun" within the past week. Mateen had a concealed carry permit from the state of Florida allowing him to legally purchase a firearm in the state, a law enforcement source told Milton.
Orlando Police Chief John Mina said the suspect was armed with a handgun and an AR-15-style assault rifle. There's no current indication that Mateen had accomplices, police say.
He worked as a security guard and worshiped at an Islamic Center
Mateen worked as a security guard, and was employed by G4S Security since Sept. 10, 2007. In a statement, G4S said they are "shocked and saddened by the tragic event" and are cooperating with law enforcement.
CBS News confirmed that Mateen worshiped at the Islamic Center in Fort Pierce, about 15 miles north of Port St. Lucie and 120 miles south of Orlando.
Imam Syed Shafeeq Rahman said although Mateen was not very social, he also showed no signs of violence, Rahman said. He said he last saw Mateen on Friday.
"When he finished prayer he would just leave," Rahman told The Associated Press. "He would not socialize with anybody. He would be quiet. He would be very peaceful."
Men at the mosque who didn't want to be identified told CBS News they have known Mateen for about five years and that he would come to the center with his son, a 3-year-old, to pray. They described Mateen as a devoted father and family man and said there was no indication that he would do something like this.
The Islamic Center released a statement condemning the attack, calling it "monstrous."
"The Muslim community of Fort Pierce joins our fellow Americans in repudiating anyone or any group that would claim to justify or excuse such an appalling act of violence," the statement read.
A law enforcement official has confirmed to CBS news senior investigative producer Pat Milton that Mateen made the Hajj, an Islamic pilgrimage to Mecca, Saudi Arabia in March 2012. He made another foreign trip to Dubai in 2011, a U.S. intelligence source tells CBS News' Tepper.
He allegedly abused his former wife
The suspect had been married to Sitora Yusufiy for several months before divorcing in 2011, Milton reports.
"He was mentally unstable and mentally ill," Yusufiy told reporters in Boulder, Colorado. Although records show the couple didn't divorce for two years after the marriage, Yusiufiy said she was actually only with Mateen for four months because he was abusive. She said he would not let her speak to her family and that family members had to come and literally pull her out of his arms.
Yusufiy said she was "devastated, shocked, started shaking and crying" when she heard about the shooting, but she attributed the violence to his mental illness, not any alliance with terrorist groups.
"My personal opinion is that this has nothing to do with ISIS," he said.
Mateen had no criminal record, but Yusufiy said he owned a pistol. She said he wanted to be a police officer and had applied to the police academy.
A New Jersey man who identified himself as Yusufiy's father and Mateen's former father-in-law told CBS News his daughter was married to Mateen seven years ago. He said the two met online and had only known each other for a few months when she moved to Florida and married him.
"When we even heard that, we actually didn't like that," said the man, who didn't give his name. "Because we are people who believe in conservative traditions, and we said you know it's weird that you know this person for two to three months online."
The man said Mateen became abusive towards his daughter. The family went to Florida in September 2009 to pick up their daughter and called police to get her belongings, he said. She later filed for divorce.
Since then, the woman and her family have had no contact with Mateen, he said.
The family is from Uzbekistan and came to the U.S. in 1999, the man said. He said he was surprised to learn Mateen was the gunman.
"I was really shocked, why would he do such a thing? So many people," the man said.
Officials piecing together a profile
Officials are trying to piece together who the suspect was and hone in on his online footprint. A law enforcement source tells Milton investigators are seeking court authorized search warrants for the suspect's home, car, and communication devices including his cell phone and computer. Police have said the suspect was driving a van that was found outside the nightclub.
They are also seeking Mateen's financial records and phone records to determine who he may have been in contact with, including anyone overseas.
Allegations of anti-gay leanings amid investigation into possible hate motivation
The suspect's father has spoken out to the media, saying his son was anti-gay and he doesn't believe the attack was motivated by religion. Florida Rep. Alan Grayson said he believes the attack was "ideologically motivated."
Sources tell Milton that authorities investigating the incident are still looking into whether the attack is a hate crime. But Grayson said he believes "it's no coincidence that the attack took place where it did and when it did."
"It might be that we've seen the commission of an awful hate crime last night," Grayson said.