The autopsy of the gunman who massacred 49 people in a Florida nightclub attack last month revealed he was HIV-negative and likely a long-term user of steroids, two U.S. law enforcement officials said.
The revelation comes as FBI agents continue to scour the background of Omar Mateen for clues as to why he launched his June 12 rampage at Orlando's Pulse nightclub, the deadliest mass shooting in U.S. history.
The 29-year-old had became radicalized in recent years, FBI officials have said, and pledged allegiance to Islamic State militants during his attack.
Federal investigators are not sure if steroids played a role in the shooting. A medical examiner found evidence of physical changes to Mateen's body that were consistent with long-term steroid use, the officials said, and is seeking to confirm that assessment through further testing.
The National Institute on Drug Abuse reports on its website that using high doses of steroids, which help build body mass and muscle, "increase irritability and aggression. Some steroid abusers report that they have committed aggressive acts, such as physical fighting or armed robbery, theft, vandalism, or burglary."
A spokeswoman for the Orange County, Fla. medical examiner declined to comment on the preliminary findings.
"Whether or not an individual used steroids can be determined through specimen tests," Carrie Proudfit, the spokeswoman wrote in an email. "Toxicology reports would reflect those results. They'll be made available to law enforcement."
Proudfit referred further questions to the FBI. Bureau spokeswoman Carol Cratty declined to comment.
The results, if confirmed through further testing, would not be entirely surprising. Mateen's ex-wife, Sitora Yusufiy, told reporters shortly after the shooting that the former security guard had a history of steroid use. A former coworker of Mateen's told CBS News that the gunman told him in 2006 that he had started using steroids.
The law enforcement officials also disclosed that the autopsy determined that Mateen was HIV-negative.
On June 21, Spanish-language television network Univision aired a report in which "Miguel," a man wearing a disguise to conceal his identity, alleged that he had sex with Mateen after meeting him on a gay dating app. Miguel said Mateen had sex with other men too, including a threesome with a Puerto Rican who allegedly told Mateen, after having had unprotected sex with him, that he was HIV-positive.
Several Pulse regulars have also come forward, claiming to have seen Mateen at the club or to have been contacted by him on the gay dating apps Grindr, Jack'd and Adam4Adam.
The FBI, however, has been unable to find evidence to corroborate such claims. Agents have failed to find any photographs, text messages, smartphone apps, gay pornography or cell-tower location data that suggest that Mateen -- who was twice married to women and had a young son -- had a secret gay life, law enforcement officials have told The Times.