Another American community has been left reeling after a mass shooting, with 12 dead after a gunman opened fire at a western themed bar in Thousand Oaks, California.

The shooting began late Wednesday night in the Borderline Bar & Grill, sending people diving under pool tables and other furniture for cover. Witnesses and victims said that stools were thrown through windows to enable bar patrons to get away from the hail of bullets.

A college country music night was underway when the gunman - dressed in black - shot a security guard who was standing outside the bar before entering. Witnesses suggested a smoke grenade may have been thrown.

The shooting comes less than two weeks after 11 were gunned down at the Tree of Life Synagogue in Pittsburgh, Pennsylvania. A number of members of congress swiftly called for new gun control legislation in the wake of the latest tragedy. Such calls have had little effect in recent years.

Officials identified Ian David Long, of nearby Newbury Park, California, as the suspected shooter. Long was killed at the bar, and police said he carried out the massacre with a legal .45-calibre handgun that he had fitted with an extended magazine illegal in California. He had apparently shot himself.

“It’s a horrific scene in there,” Ventura County Sheriff Geoff Dean said. “There’s blood everywhere.”

Long, a 28-year-old Marine veteran who may have been suffering from PTSD according to reports, had purchased the rifle legally, and burst into the bar at around 11.20pm. He had driven his mother’s car there, and did not say anything before turning his weapon into the crowd, according to witnesses.

Cole Knapp, 19, said he saw the gunman walk in and stop at the counter as if to pay. Then Mr Knapp said 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 told Reuters.

Knapp said he first helped people hide behind a pool table and then fled to the bar’s outdoor smoking patio, where people were unaware of the shooting, and urged them to run.

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Police first began identifying victims of the Thousand Oaks attack less than 12 hours after the gunman’s last shot rang out, including Sergeant Ron Helus, a 29-year veteran of the Ventura County Sheriff’s Office. In a press conference on Thursday, Mr Dean praised the work of his office — including the sacrifice from Mr Helus — for working fast in response to the shooting at the packed college night bar. At least five off-duty law enforcement officers helped to protect people.

“It could have been much, much worse,” Mr Dean said on Thursday, just a day before he was set to retire. He added that he had been told there were 150 to 200 people in the bar, which is popular with students.

Mr Dean said that his Sheriff’s Office was mourning the loss of Mr Helus, who was married and had a son. The 54-year-old had been with the force for nearly three decades, and was close to retirement.

“He went in there to save people and made the ultimate sacrifice,” Mr Dean said. He noted that Mr Helus frequently talked to his wife during his shifts, and had spoken with her shortly before he entered the bar. “Hey, I have to go handle a call,” he was said to have told his wife. “I love you. I’ll talk to you later.”

Cody Coffman, 22, was also killed, according to his father Jason. Mr Coffman broke down as he told reporters how his last words to his son as he went out that night were not to drink and drive and that he loved him. He added: “Oh Cody, I love you son.”

The family of 23-year-old Justin Meek, who was also killed according to California Lutheran University president Chris Kimball, said in a statement that Mr Meek ”heroically saved lives”.

Another victim, Alaina Housley was just 18, and was a promising student at Pepperdine University with plans to study law, her family said.

Adam Housley, a former Fox News correspondent, and Tamera Mowry-Housley, an actress known for the 1990s TV series Sister Sister, said their niece was killed at the bar where she had gone line dancing with friends.

Other victims include Noel Sparks who was a youth camp leader and Moorpark College student. The death was announced by United Methodist Church Westlake Village. "It is with heavy hearts that we notify you that Noel Sparks was among the victims of last night's shooting. We grieve with Tony Sparks and Wendy Anderson," the church said in a statement.

Daniel Manrique, 33, was a Marine veteran and focused on helping other veterans adjust to civilian life, according to friends. “I have no doubt that he died a hero, shielding others from gunshots. He will forever be our hero, son, brother, and the best uncle anybody could ever ask for,” Gladys Manrique Kosack, a family member said.

Telemachus Orfanos was identified by his mother who said the he had survived the mass shooting in Las Vegas last year. Jake Dunham and Blake Dingman, both 21, were identified by local Los Angeles outlet ABC7.

Sean Adler, a bouncer at the bar and former wrestling coach at Simi Valley High School, perished in the California shooting and was remembered by the local wrestling community.

“He was positive, motivational, and truly wanted the best for the people around him,” read a post on the Royal Wrestling Facebook page. “He was one of the victims last night at the shooting at Borderline Bar and Grill where he worked as a bouncer.”

In response to the shooting, president Donald Trump tweeted that he had been fully briefed on the incident, and ordered federal flags at half staff to mourn the dead.

The shooter had served in the marines from 2008 until 2013, and was a machine gunner. He had earned the rank of corporal in 2011, and had received other accolades including a Combat Action Ribbon and a Marine Corps Good Conduct Medal.

At an afternoon press conference, police said it would be “premature” to speculate on any possible motive and are working to “paint a picture of the mind” of Long. Officials did not have any comment on reports indicating the suspect may have suffered from PTSD. ”Obviously he had something going on in his head that would cause him to do something like this,” Sheriff Dean had said earlier in the day. “Obviously he had some sort of issues.”

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Mr Dean told reporters that officers had gone to Long’s home in nearby Newbury Park, about four miles from the bar, in April to answer a disturbance call and found him to be agitated. Mental health specialists talked with Long and determined that no further action was necessary.

But, in his southern California neighbourhood where he lived with his mother, neighbours and police records shed some light on the life of the decorated combat veteran of the Afghanistan war.

Long had several interactions with police over the years, and a neighbour said that the entire neighbourhood was aware of the issues, and that his mother had been frustrated that her son was not seeking help.

Richard Berge, one of those neighbours, told USA Today that he had become friendly with the mother after offering to care for the family’s German shepherds. He had not been inside the Long house but told that newspaper another neighbour had seen walls “full of holes”, which appeared to have been caused by kicking.

Long had been the victim of a battery at a local bar in Thousand Oaks, and had been involved in two traffic incidents. Deputies were once called to his house last year as a result of a domestic dispute, and found that Long was acting “somewhat irate and acting irrationally”.

Police said they are still processing the Long’s vehicle and home and are not yet disclosing any possible evidence they uncovered.

California governor-elect Gavin Newsom, who won the governor’s race on Tuesday, made clear that change needs to happen.

“This is America… this doesn’t happen anywhere else on the planet,” he said. “We can’t let folks forget that. We can’t allow this to be normalised.”

In Washington DC, a number of Democrats – newly empowered after taking control of the House during this week’s midterm elections – vowed action on gun control, an issue that politicians on Capitol Hill have notoriously failed or refused to address.

Congressman Jim Himes, whose home state of Connecticut endured the deadly Sandy Hook Elementary School shooting in 2012, also attacked the lack of action on gun control. He told CNN: “I’m embarrassed to say…my first thought was, ‘Here we go again, it’s this week’s mass shooting’, and that’s a really hard way to think about this. I contrast where we are today with how we all felt about Sandy Hook.”

He added: “This is a weekly thing [and] even though it’s become a weekly thing, nobody does anything, especially the congress where I work.

“35,000 Americans dead a year as a result of gun violence and congress can’t even find its way to studying the problem.”

Senator Kamala Harris — who represents California — mourned the loss and called for action on gun control measures.