The gunman responsible for killing 12 people, including a police officer, in a mass shooting at a Thousand Oaks, California, bar on Wednesday night was a Marine veteran who had previous contact with law enforcement and may have been suffering from Post-Traumatic Street Disorder.

CBS News reports that David Ian Long was found dead of what may have been a self-inflicted gunshot wound at the scene, and is believed to have been the gunman who killed a dozen people. While CBS News reports that Long as 28, multiple outlets have reported his age as 29.

According to the report, investigators found evidence at the scene of the mass shooting that led them to a home in Newbury Park, California, though authorities are still working to confirm the shooter lived there.

Long had previously served in the U.S. Marine Corps, according to CBS News.

Sheriff Geoff Dean told the Los Angeles Times that Long was known to law enforcement, and that police had most recently had contact with the suspected gunman in April. Officers reportedly responded to a complaint that he had been disturbing the peace, and noted that he appeared to be angry and irrational. Still, a mental health evaluation reportedly determined that Long did not need to be taken into custody.

Neighbor Richard Berge, 77, told the newspaper that he believed Long had PTSD and caused a lot of problems for his mother, who he lived with.

“She’s a very sweet woman, but she had a lot of problems with the son,” Berge told the Los Angeles Times. “I just know he tore the house up.”

Investigators have not yet determined a motive for the shooting.