Authorities have identified the gunman who killed 12 people late Wednesday during an attack at a southern California bar and dance club as 28 year-old Ian David Long.
Ventura County Sheriff Geoff Dean told reporters Long was a former U.S. Marine who had minor encounters with law enforcement in recent years, including a traffic accident and an incident when Long was beaten at a bar.
Dean said officers responded to a disturbance call at Long's home in April and Long "was somewhat irate, acting a little irrationally." Mental health personnel spoke with Long, Dean said, but they did not feel he qualified for detention under a state law. Dean said officials suspected he suffered from post-traumatic stress disorder because of his military background.Dean said law enforcement authorities have not uncovered a motive for the Wednesday attack on the Borderline Bar & Grill in the city of Thousand Oaks but the gunman "obviously had some sort of issues."
Long was found dead in the club, according to Dean.
"We believe he shot himself. When the officers went in and made reentry, they found him already deceased," he said.
The mass shooting occurred after Long entered the club armed with a handgun and smoke bombs. The club, a popular place for students from California Lutheran University, was hosting a "college night" event at a country music bar at the time of the shooting. The bar is less than 8 kilometers from the university and also near several other universities.
Dean told reporters earlier one of the first officers to arrive was shot after going inside to confront the shooter.
He said Sheriff Sgt. Ron Helus, a 29-year veteran of the department, was immediately hit with numerous gunshots and later died after being taken to a hospital.
"I told his wife he died a hero," Dean said of Helus, who had a wife and a son and planned to retire next year.
Multiple people were injured in the attack as well, but Dean said the exact number was unclear because a number of them had taken themselves to hospitals for treatment.
"It's a horrific incident," Dean said. "It's part of the horrors that are happening in our country and everywhere, and I think it's impossible to put any logic or any sense to the senseless."
Eyewitnesses described a scene of chaos as shots rang out in the dance club and patrons scrambled to seek cover and escape. Witness John Hedge told ABC News he was near the front door when the shooting started.
"I just started hearing these big pops. Pop pop pop," he said. "I hit the ground. I look up. The security guard ... was shot, he was down. The gunman was throwing smoke grenades all over the place. I saw him point to the back at the cash register and he just kept firing."
The U.S. Marine Corps issued a statement extending "its deepest condolences to the families of the victims in this senseless tragedy." The Marine Corps said Long attained the rank of corporal after serving nearly five years, including seven months in the war in Afghanistan. He was a machine gunner and the recipient of numerous medals, including the Good Conduct Medal and the Combat Action Ribbon.
U.S. President Donald Trump wrote on Twitter early Thursday he has been "fully briefed" on the shooting, applauded the response of law enforcers and extended blessings to the victims and their families.
Trump, who has resisted efforts to pass more stringent gun control laws, also ordered American flags flown at half-staff in honor of the victims.
The top Democrat on the House Judiciary Committee, Jerry Nadler, said lawmakers would start crafting gun-control legislation when the House of Representatives convenes with a Democratic majority in early January.
"We must find a way to stop the senseless, and many times preventable killings that are robbing our country of innocent lives," he tweeted.
The shooting was the deadliest mass shooting since 17 students and teachers were killed at a Parkland, Florida high school nine months ago. It comes just days after a gunman massacred 11 people at a synagogue in Pittsburgh, Pennsylvania. The suspect in that case, 46-year-old Robert Bowers, has pleaded not guilty to federal charges. Prosecutors are seeking the death penalty.
Shootings are very rare in Thousand Oaks, a city of about 130,000 people about 64 kilometers west of Los Angeles. Thousand Oaks was considered the third-safest city in the U.S. this year, according to Niche, an online company that provides data on neighborhoods, companies and schools.
Carla Babb contributed to this report.