The gunman who killed 12 people at a country music bar in California fired a bullet through the wall of his mother's home during a volatile row in April and spent hours holed up inside until police coaxed him out but he was cleared by mental health officials and was somehow still allowed to own the Glock 45. used in Wednesday's attack.

In April, police were called to Ian Long's home in Newbury Park after neighbors heard loud crashes coming from inside the house he shared with his mother Colleen.

She lived 'in fear' of him, the neighbors said, adding that Long, who friends have described as 'cocky', was 'hell to live with.'

The neighbors already suspected that he was suffering from PTSD after returning from a tour of Afghanistan between 2010 and 2011 and say he was disrespectful and rude whenever he passed them in the street.

When police arrived at the home, they called in mental health specialists to help resolve the situation and, according to The Wall Street Journal, it took hours for them to get Long out of the house.

Inside, furniture had been tossed all over the house and there were holes in the wall including the one caused by a bullet, they said.

Ian Long, 29, killed himself after killing 12 people at the Borderline Bar and Grill in Thousand Oaks on Wednesday night. His mother Colleen is shown, right, on Thursday at their home. Neighbors say he 'terrified' her and was 'hell to live with'

'They couldn’t get him out for a long time, like half the day,' neighbor Richard Berge said on Thursday.

They had heard gunshots, they said, coming from inside the home and there was a bullet hole in the wall.

Despite the combination of red flags, the mental health specialists who responded decided that Long was not suitable to be involuntarily committed under Section 5150 of the California Welfare and Institutions Code.

He was never arrested and continued living in his mother's home until Wednesday night's attack.

Police are yet to reveal why he was not committed after that April incident.

The law states that any qualified officer or clinician can confine a person who they suspect has a mental disorder if they are a danger to themselves, others or are 'gravely' disabled.

A spokesman for Veterans Affairs told DailyMail.com on Friday that Long was never enrolled in any of its healthcare programs.

It is also unclear if Long bought the Glock .45 he used in Wednesday's attack before or after the April incident or if it was the same one he used to put a bullet through the wall.

The gun was legally purchased but Long, who was a machine gunner in the Marines, had modified its magazine so that it could hold 30 rounds, three times the legal limit.

He enlisted in the Marines in 2008 when he was 18 after being told that his dreams of playing professional baseball would never come to fruition.

In April, police went to the family's home in Newbury Park after hearing loud crashes and a gunshot. Long spent hours inside before being coaxed out by police but was not arrested and was cleared by mental health specialists

Long (left and right) was a machine gunner in the Marines Corps and served until 2013 when he was given honorable discharge. He was deployed once to Afghanistan and received 10, standard-issue medals during his service

In high school, Long saw no other career for himself and wrote in his yearbook that the only thing he saw in his future aside from the sport was 'death'.

GUNMAN'S MARINE RECORD 2008: Long joins the Marines on August 4, 2008. He was 18 at the time. Nov. 16, 2010 - Jun. 14, 2011: Deployed to Afghanistan as part of Operation Enduring Freedom August 11, 2011: His rank is listed as Corporal after his tour 2011-2013: His last known assignment was in the 2nd Battalion, 3rd Marine Regiment, Third Marine Division, based out of Kaneohe Bay, Hawaii. March 3, 2013: Long leaves the Marines. The circumstances are unknown. 2013 - 2016: Long studies at the California State University Northridge and majors in athletic training Advertisement

But his baseball coach has since revealed he was no remarkable talent and did not even frequently start in the school's varsity team.

The coach, Scott Drootin, said he had a few friends but was not one to joke around with his teammates.

Long spent five years in the armed forces as a machine gunner.

According to a Rebekah Homokay, a former friend and classmate, he 'loved guns' and set his sights on the Marines after his baseball dreams fell apart.

'The Marines, that was his goal. He loved America and he loved guns,' she said.

She said he was a 'cocky guy' and was 'one of those bros that drove a huge car to high school,' she added.

Long's history and how he was able to own the gun are now part of the FBI's investigation into the massacre.

He shot himself after Wednesday night's massacre.

On Friday morning, President Trump said the shooting was 'horrible' and made him 'sick'.

'It's a disastrous problem it makes you sick to look at it. He was a war veteran, he saw some pretty bad things.

'A lot of people say he had the PTSD. That's a tough deal. It's a horrible thing. They come back, they're never the same,' he said.