WASHINGTON (Reuters) - As families grieved on Sunday, a picture began to emerge of the man identified as the shooter who killed 50 people at a packed gay nightclub in Florida on Sunday (June 12). He was described as quiet with friends and had been interviewed by the authorities in recent years for suspected sympathies with Muslim extremists.
He also had worked for G4S, the world's largest security services firm, since 2007, and carried a gun as part of his duties, the company said on Sunday.
Police killed the shooter, identified as Omar Mateen, 29, a Florida resident and United States citizen who was the son of immigrants from Afghanistan.
He had legally purchased the firearms within the last week, Mr Trevor Velinor, Assistant Special Agent In Charge of the Bureau of Alcohol, Tobacco, Firearms and Explosives Tampa Field Office, was quoted by the City of Orlando website as saying.
"He was an armed security officer," said G4S spokesman David Satterfield. G4S said in a statement that Mateen had been employed by the company since Sept 10, 2007.
G4S provides security to federal buildings in Florida. It was unclear if Mateen had access to them. Mr Satterfield said G4S was trying to ascertain whether any guns used in the attack were related to Mateen's work.
"A lot of that is dependent on what law enforcement is releasing," he said.
Another spokesman said Mateen had undergone screening by his employer in 2007 and 2013, with both checks revealing nothing of concern.
"Mateen underwent company screening and background checks when he was recruited in 2007 and the check revealed nothing of concern," a company spokesman said in a statement. "His screening was repeated in 2013 with no findings."
The company learnt in 2013 that Mateen had been questioned by the FBI but that the inquiries were then closed, the spokesman said. The firm was unaware of any alleged connections between Mateen and terrorist activities, or any further FBI investigations, she said.
An FBI spokesman said on Sunday that FBI agents had twice interviewed Mateen in 2013 and 2014 after he made comments to co-workers indicating he supported militant groups, a process likely to renew questions over whether the US government has a clear strategy or adequate resources to turn Americans away from radicalism.
The first investigation took place in 2013 when Mateen made inflammatory comments to co-workers that indicated sympathy for militants, FBI special agent in charge Ron Hopper told a news conference in Orlando.
He was investigated and interviewed twice but the FBI was"unable to verify the substance of his comments", Agent Hopper said. In 2014, Agent Hopper said, Mateen was investigated and interviewed again, this time for suspected connections to Moner Mohammad Abu-Salha, an American citizen who became a suicide bomber in Syria in 2014.
"Hopper said Mateen's contact with Abu-Sallah was minimal and it was deemed that "he did not constitute a substantive threat at that time".
Agent Hopper said Mateen was not under investigation or surveillance at the time of Sunday's attack.
Agent Hopper said Mateen called during the massacre to pledge allegiance to the Islamic State in Iraq and Syria (ISIS), which in recent years declared a caliphate over large swaths of Iraq and Syria. But the depth of that commitment is unclear.
One US counterterrorism official said there was "no evidence yet that this was directed or connected to ISIS".
"So far as we know at this time, his first direct contact was a pledge of bayat (loyalty) he made during the massacre," said the official, referring to the call moments before the shooting.
Mateen also mentioned the Boston Marathon bombers during the call, which he made 20 minutes into the shootings, the authorities said.
Mr Satterfield said G4S was still gathering information on any contacts employees or the firm might have had with the FBI regarding Mateen.
Mateen was assigned to guard the PGA Village golf club in Port St. Lucie, Florida, according to local newspaper TC Palm.
Mr Daniel Kime, a security guard employed along with Mateen by the security firm G4S in the Fort Pierce area, said he met Mateen briefly three or four times and did not know him well.
"Every time I saw him he never smiled. If you said good morning, he'd just walk right by you, like he had a chip on his shoulder," Mr Kime said.
G4S, which employs 620,000 people and operates in more than 110 countries, offers services ranging from managing jails to protecting sports stars.
The company is also no stranger to controversy. It has come under fire from rights advocates for providing services to Israeli prisons holding Palestinian detainees, and in 2014 the Bill and Melinda Gates Foundation said it sold its stake in G4S.
Three of the firm's security guards were acquitted of manslaughter charges in 2014 in the cardiac arrest death of an Angolan aboard a flight from London who they were repatriating to his native country.
The British government in 2014 said G4S would repay US$181 million for overcharging it on a contract to tag criminals with monitoring devices.
Mateen appeared to live a quiet life in Fort Pierce on Florida's south-east coast, 195km from the nightclub where the massacre took place.
The imam of the Florida mosque that Mateen attended for nearly 10 years described him as a soft-spoken man who would visit regularly but rarely interact with the congregation.
"He hardly had any friends," Syed Shafeeq Rahman, who heads the Islamic Center of Fort Pierce, told Reuters. "He would come with his little son at night to pray and after he would leave."
Imam Rahman said Mateen never approached him regarding any concerns about homosexuals. Imam Rahman said he himself had been increasingly speaking out against violence, noting that even inflicting a scratch on someone was against the tenets of Islam.
The tragedy had left the local Muslim community fearful, he said. "We thought we could relax for a couple of years and tell people we are normal human beings," Imam Rahman said.
Imam Rahman said he planned to add extra security to the mosque and brighter lighting to help reassure followers they were safe amid fears of a public backlash against Muslims.
Still, much remains unclear about the motivations of Mateen. He was born in New York of Afghan descent. A classmate from his Florida high school described him as a typical teenager who played football for a Martin County team in Stuart, a small city about a 20-minute drive from Fort Pierce.
Mr Samuel King said he often spoke with Mateen after he graduated high school. Mr King worked at Ruby Tuesday's restaurant in the Treasure Coast Mall, where Mateen worked at GNC, the nutrition store, he said.
Mr King, who is openly gay, said the Mateen he knew until 2009 did not appear to be anti-gay.
"What is shocking to me is that the majority of the staff at Ruby Tuesday's when I worked there were gay. He clearly was not anti-(gay) at least not back then. He did not show any hatred to any of us. He treated us all like the individuals we were. He always smiled and said hello."
Mr King described Mateen as gregarious and talkative in the immediate years after high school, but said "something must have changed" since he last saw him in 2009.
Mateen's father, Mir Seddique, told NBC News the massacre was not related to religion.
He said his son turned angry when he saw two men kissing in Miami a couple of months ago.
Mateen's former wife, who spoke to The Washington Post, said her former husband was violent and mentally ill and beat her repeatedly while they were married.
Ms Sitora Yusufiy said she met Mateen online about eight years ago and decided to move to Florida to marry him, according to The Washington Post.
"He was not a stable person," she said. "He beat me. He would just come home and start beating me up because the laundry wasn't finished or something like that."
She also said he was emotionally and mentally disturbed with a violent temper, yet aspired to be a police officer.
Ms Yusufiy also told reporters in a news conference aired on CNN that she was "rescued" by family members from her former husband after four months of a stormy marriage that ended in divorce.
Mateen had a Florida firearms licence that expired in 2013 and a state permit to work as a security guard, according to public records. He was registered as a Democrat.
City, state and federal officials were searching Mateen's apartment in the Woodlands condominium building in Fort Pierce and had told other residents to evacuate.