The Monterey gunman was a dance teacher who taught at the centre of the massacre "almost every night."
Huu Can Tran, 72, who killed ten people during Chinese Lunar New Year celebrations on Saturday, taught dance lessons at the Star Ballroom Dance Studio in the early 2000s for nearly five times a week.
He lived five minutes away in the San Gabriel Valley and was "hostile to a lot of people" at the studio, according to Tran's friends.
The gunman's pals, who were close to the mass shooter in the early 2010s, told CNN Tran believed many of the students said "evil things about him."
Tran also met his ex-wife at the studio after he offered her free dance lessons and they quickly married after the pair hit it off.
However she admitted she lost her love of dancing as he would get angry when she made a mistake with the choreography.
The gunman's ex-wife, whose identity hasn't been revealed, filed for divorce in 2005 from Tran just a short while after they tied the knot.
The shooter stopped teaching lessons at the studio, according to his friends, when he relocated to Hemet in 2013 after spending 20 years in Los Angeles.
Many of Tran's friends lost contact with him at around the time he relocated - with many stunned at his actions.
Apart from being a dance teacher, Tran was a registered truck driver who had his own business called Tran's Trucking Inc, which ran from 2002-2004, according to CNN.
The mass shooting saw five women and five men shot dead and wounded a further ten.
During a standoff with cops Tran died from a self-inflicted gunshot wound.
One friend admitted it didn't take much for Tran to get angry and he had trust issues, it is claimed.
The mass shooter started his massacre at the Star Ballroom Dance Studio before he turned up to the Lai Lai Ballroom in nearby Alhambra just 30 minutes later.
Heroic witnesses fought Tran off and were able to take his gun.
He then quickly left the scene and was a wanted man on Sunday until cops found the van he used to flee the shooting.
The gunman's motive is unknown but he intended to kill more people, according to Los Angeles County Sheriff Robert Luna.
He said at a press conference yesterday: "He intended to kill more people."
Sheriff Luna praised the nearby witnesses who stepped in, he added: "They saved lives. This could've been much worse."
The ages of the victims have not been disclosed by police but Luna believes they are all over 50 - as seven of the wounded victims remain in hospital.
Tran was a carrying a semi-automatic pistol with an extended magazine. A second handgun was found in his van where he was found dead, according to police.
On Sunday, authorities entered his van after surrounding it for hours when they heard a gunshot and found Tran slumped on the steering wheel.
Police had been searching for a white van after eyewitnesses reported seeing the van flee from Alhambra.
