A former US Marine combat veteran opened fire in a Los Angeles area bar and dance hall filled with college students, killing 12 people in a mass shooting that stunned a Southern California community with a reputation for safety.
The gunman, identified by police as 28-year-old Ian David Long, was found dead of an apparently self-inflicted gunshot wound following the Wednesday night massacre at the Borderline Bar and Grill in Thousand Oaks, a suburb 40 miles (64 km) northwest of Los Angeles, law enforcement officials said.
Paul Delacourt, assistant director in charge of the Los Angeles FBI, told a news conference that it was too early to speculate on the gunman's motives but that he appeared to have acted alone.
"We will be sure to paint a picture of the state of mind of the subject and do our best to identify a motivation," Delacourt said, adding that the FBI would investigate any possible "radicalisation" or links to militant groups.
Long opened fire seemingly at random inside the Western-themed bar at about 11:30 pm PST (0730 GMT Thursday), using a .45 caliber Glock handgun equipped with a high-capacity magazine, Ventura County Sheriff Geoff Dean said.
Long was in the Marine Corps from 2008 to 2013, reaching the rank of corporal and serving as a machine gunner in Afghanistan.
The sheriff said it was possible that Long had suffered from post-traumatic stress disorder.
"Obviously he had something going on in his head that would cause him to do something like this," Dean said.
Dean told reporters that in April officers had gone to Long's home in nearby Newbury Park, about 4 miles (6 km) from the bar to answer a disturbance call and found him agitated.
Mental health specialists talked with Long and determined that no further action was necessary.
Dean said he had been told that 150 to 200 people were in the Borderline at the time. "It could have been much, much worse."
Asked what the scene inside the bar was like, Dean said, "Like ... hell."
Earlier he had described it as "a horrific scene in there. There is blood everywhere and the suspect is part of that."
Dean estimated 10 to 15 people, including one with a gunshot wound, had gone to hospitals.
Security guard, sheriff’s deputy shot
The massacre was the latest mass killing in the United States and was sure to revive the debate on gun control.
After a man fatally shot 11 worshipers at a Pittsburgh synagogue last month, US President Donald Trump said their deaths could have been prevented if there had been an armed guard inside the temple.
Long shot an unarmed security guard outside the bar before going inside, where he shot more security staff, CNN reported.
Ventura County Sheriff's Office Sergeant Ron Helus, a 29-year veteran with a wife and son, was shot and killed inside.
Trump ordered flags to be flown at half-staff at public buildings and grounds.
The Borderline is popular with students and on Wednesday night had hosted College Country Night. California Lutheran University, about five miles from the bar, cancelled classes on Thursday.
Pepperdine University, about 20 miles away, planned a prayer service.
Bar patron Cole Knapp, 19, told Reuters he saw the gunman walk in and stop at the counter as if to pay a cover charge.
Then Knapp heard gunfire and saw a young woman at the counter shot repeatedly.
"It took a couple of seconds for people to realise what was going on and once that happened it was just utter chaos," he said.
Knapp said he helped people hide behind a pool table and then fled outside, alerting people on an outdoor smoking patio.
Knapp said he and a friend helped carry a gunshot victim to an ambulance.
Thousand Oaks, with a population of about 127,000, is a leafy, sprawling suburb named the third safest city in the United States for 2018 by the Niche research company.
"I've learned it doesn't matter what community you're in,” Dean told reporters when asked if he was surprised this happened in Thousand Oaks.
"It doesn’t matter how safe your community is. It can happen anywhere."
The names of the victims were not immediately made public and people gathered at a nearby teen centre waiting to learn the fate of loved ones.
Jason Coffman, wept as he told reporters that his son, Cody, 22, was among the dead.
"Only him and I know how I love, how much I miss him," he said. "Oh, son, I love you so much."
Actress Tamera Mowry-Housley confirmed in a statement to ABC News that her niece, Alaina, was killed at the bar.
Among those outside the hospital was Ellen Rivera, who said she had survived the October 2017 slaughter of 58 people at an outdoor concert in Las Vegas - the worst mass shooting in US history.
(Reporting by Alex Dobuzinskis; Additional reporting by Dan Whitcomb in Los Angeles, Bernie Woodall in Ft. Lauderdale, Fla., Rich McKay in Atlanta, Doina Chiacu in Washington, D.C. and Gina Cherelus and Gabriella Borter in New York; Writing by Bill Trott and Dan Whitcomb; editing by Jeffrey Benkoe and Grant McCool)