An ex-marine who opened fire on students in a bar in Thousand Oaks, California was cleared by mental health specialists in April, according to a Ventura County official.

Sheriff Geoff Dean said officers went to the home of the gunman – identified as Ian David Long, 28 – in nearby Newbury Park in April to answer a disturbance call and found him to be agitated.

Mental health workers talked with ex-marine Long and determined that no further action was necessary.

No motive has yet been determined, according to Sheriff Dean, but eyewitness accounts are emerging of the horror and confusion inside the Borderline Bar and Grill after an ex-marine opened fire on students.

Bar patron Cole Knapp, 19, said he saw the gunman walk in and stop at the counter of the bar on Wednesday night (local time) to pay a cover charge.

Mr Knapp then witnessed the man repeatedly shoot a young woman.

Despite Ventura County being named the US’s third safest city for 2018, Sheriff Dean told a news conference on Friday (AEST) he wasn’t surprised the shooting happened in Thousand Oaks.

“It doesn’t matter how safe your community is. It can happen anywhere,” Sheriff Dean said.

Armed with a .45-calibre Glock handgun with an extra-capacity magazine, Long fired randomly inside the bar where up to 200 students were enjoying a regular ‘College Country Nights’ gathering.

“It took a couple of seconds for people to realise what was going on and once that happened it was just utter chaos,” Mr Knapp said.

As relatives continue to identify loved ones killed in what is now the 307th mass shooting in the US this year, according to Gun Violence Archive, more details are emerging about Long’s background.

Long was in the Marine Corps from 2008 to 2013, reaching the rank of corporal, and served as a machine gunner who was deployed to Afghanistan for eight months.

Sheriff Dean said it was possible that Long had suffered from post-traumatic stress disorder. Authorities say Long apparently took his own life.

In the hours after the shooting, police raided Long’s home, about 8km from the Borderline, where he lived with his mother, CBS News reported.

One neighbour Donald Macleod told CBS he heard loud arguments across his backyard fence.

“He was a lot worse when he came back from the military.

“I suspected he had a gun there because I heard a gunshot one night, over a year ago,” he recounted.

The FBI’s Paul Delacourt told reporters on Friday (AEST) that it was “too premature to speculate” on Long’s motive.

He said evidence gathered from the crime scene and from the gunman’s home and car were being processed for evidence.

Survivors share stories of survival as victims identified

Mr 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.

Once outside, Mr Knapp and a friend helped carry a gunshot victim to an ambulance.

Names of the victims were not immediately made public after the shooting and about 60 people were gathered at a teen centre in Thousand Oaks waiting to learn if their loved ones were among the dead.

After families were briefed, one man sat outside on the curb sobbing loudly.

Cody Coffman, 22, has been identified by his father, Jason, the ABC reported. His grandfather spoke to reporters after Cody was identified.

“Life is sacred and we should cherish it.“ We spoke w/the grandfather and father of Cody Hoffman, a young man with dreams of going to the army, whose life was heartbreakingly cut short in last night’s shooting in #ThousandOaks. 😞 We send love & healing to his family. @23ABCNews pic.twitter.com/bHObGnQwaC

— Noëlle D. Lilley (@NoelleDLilley) November 8, 2018

Ventura County Sheriff’s Office Sergeant Ron Helus, a 29-year veteran with a wife and son, was shot in the bar and died at a hospital.

A procession of at least 50 police cars and other vehicles escorted the hearse carrying his body from the hospital.

WATCH: Police, firefighters and people holding American flags lined the streets as Ventura County Sheriff’s Sgt. Ron Helus’ body was transported to the coroner’s office Thursday. https://t.co/DYN1rUPVey pic.twitter.com/MIRampM0XA

— 48 Hours (@48hours) November 8, 2018

Local bay area news station KRON4 reported Pepperdine university freshman and Napa native Alaina Housley, reported missing in the early hours after the shooting, has been confirmed dead.

Ms Housley, niece of Sister Sister actress Tamera Mowry-Housley and her husband Adam Housley, was remembered as an “incredible young woman”.

In a statement to The Hollywood Reporter, Mowry-Hously and her husband said their “hearts are broken”:

Tamera Mowry-Housley and Adam Housley's statement after learning their niece was among the #BorderlineShooting victims: "Alaina was an incredible young woman with so much life ahead of her and we are devastated that her life was cut short in this manner" https://t.co/oSVRXOTlx3 pic.twitter.com/3ZGoZuG2O1

— The Hollywood Reporter (@THR) November 8, 2018

Recent graduate of the Californian Lutheran University, Justin Meek, 23, was remembered as a hero who “saved lives in the incident”.

https://twitter.com/sawyerplaysball/status/1060627996317409280

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