Omar Mateen passed a psychological test required by his employer, security company G4S, when he was hired in 2007. Credit: Balkis Press/Sipa USA via AP Images
Undated photo or selfie of Omar Mateen, identified as the gunman in mass shooting at a gay club in Orlando, Florida on June 12, 2016. The shooting death toll rose to 50 with a further 53 wounded.
Omar Mateen, identified as the gunman in the worst mass shooting in U.S. history, had been investigated by the FBI and had an alleged history of domestic violence.Credit: Balkis Press/Sipa USA via AP Images 

UPDATE, June 13, 2016: This post has been updated to reflect that Omar Mateen worked for G4S. The number of people killed in the shooting also has been updated.

The worst mass shooting in U.S. history was carried out by a security guard licensed to carry a firearm.

Authorities have identified Omar Mateen, 29, as the gunman who left 49 people dead and more than 50 others wounded early Sunday morning at Pulse, a popular gay nightclub in Orlando, Florida.

Mateen had been investigated by the FBI and had an alleged history of domestic violence against an ex-wife, according to news reports.

His licenses to work as an armed guard were active at the time of the shooting. The Bureau of Alcohol, Tobacco, Firearms and Explosives confirmed Sunday that he recently had purchased two firearms legally.

Reveal originally checked Mateen’s arrest record in 2014 as part of an investigation into the armed security guard industry, which is regulated differently in each state. In Florida, authorities conduct criminal background checks before issuing guard licenses.

Mateen did not have a criminal record at the time. But reporters found that many guards were able to slip through the cracks of state licensing systems, including in Florida, where armed guards are not subject to mental health screenings before receiving licenses to carry firearms on the job. Reveal found many guards with histories of substance abuse who were allowed to work as armed guards.

It is unclear if Mateen had any other issues in his record, such as a record of a mental health commitment or substance abuse problems, that would have prohibited him from owning or using a gun. His ex-wife told The Washington Post that he was mentally unstable and violent.

“He was not a stable person,” she told the paper. “He beat me. He would just come home and start beating me up because the laundry wasn’t finished or something like that.”

Mateen had worked for G4S, one of the largest security companies in the United States. An in-house newsletter from 2012 identified an Omar Mateen of West Palm Beach as a guard for the company. His ex-wife told The Washington Post that he worked as a guard at a nearby facility for juvenile delinquents.

Orlando was still reeling from a very public recent killing. Christina Grimmie, who rose to fame as a contestant on NBC’s “The Voice,” was shot to death while signing autographs there Friday.

Julia B. Chan contributed to this report. Shoshana Walter can be reached at Follow her on Twitter: @shoeshine.

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Shoshana Walter

Shoshana Walter is a reporter for Reveal, covering criminal justice. She and reporter Amy Julia Harris exposed how courts across the country are sending defendants to rehabs that are little more than lucrative work camps for private industry. Their work was a finalist for the 2018 Pulitzer Prize in national reporting. It also won the Knight Award for Public Service, a Sigma Delta Chi Award for investigative reporting, and an Edward R. Murrow Award, and was a finalist for the Selden Ring, IRE and Livingston Awards. It led to numerous government investigations, two criminal probes and five federal class-action lawsuits alleging slavery, labor violations and fraud.

Walter's investigation on America's armed security guard industry revealed how armed guard licenses have been handed out to people with histories of violence, even people barred by courts from owning guns. Walter and reporter Ryan Gabrielson won the 2015 Livingston Award for Young Journalists for national reporting based on the series, which prompted new laws and an overhaul of California’s regulatory system. For her 2016 investigation about the plight of "trimmigrants," marijuana workers in California's Emerald Triangle, Walter embedded herself in illegal mountain grows and farms. There, she encountered an epidemic of sex abuse and human trafficking in the industry – and a criminal justice system focused more on the illegal drugs. The story prompted legislation, a criminal investigation and grass-roots efforts by the community, including the founding of a worker hotline and safe house.

Walter began her career as a police reporter for The Ledger in Lakeland, Florida, and previously covered violent crime and the politics of policing in Oakland, California, for The Bay Citizen. Her narrative nonfiction as a local reporter garnered a national Sigma Delta Chi Award and a Gold Medal for Public Service from the Florida Society of News Editors. A graduate of Mount Holyoke College, she has been a Dart Center Ochberg fellow for journalism and trauma at the Columbia University Graduate School of Journalism and a John Jay/Harry Frank Guggenheim fellow in criminal justice journalism. She is based in Reveal's Emeryville, California, office.