So who was Tran? Here's what we know so far:
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Law enforcement sources tell ABC News that Tran had no known criminal history.
Friends and acquaintances describe him as a quiet man who didn't get along well with many people and was quick to anger. But they also could not recall him ever getting physically violent.
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He was a regular at Star Ballroom Dance Studio, where the shooting occurred.
He also frequented the Lai Lai Ballroom and Studio in Alhambra, where he showed up after the Monterey Park shooting. At the Alhambra studio, a man wrestled a gun away from Tran when he walked through the door and he fled with no injuries.
Investigators were able to track the semi-automatic weapon left behind in Alhambra to help get the suspect's name, sources told CNN.
Records indicate Tran worked as a professional trucker for at least 20 years, for a brief time running his own trucking company.
He served as CEO of a business based in San Gabriel called Tran's Trucking, Inc. But it didn't stay in business long. Records indicate the business was formed in 2002 but dissolved in 2004.
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Tran's former wife, who asked not to be named, told CNN she met him about 20 years ago at Star Ballroom. Tran introduced himself at a dance and offered her free lessons. They married soon after that.
She said Tran had a short temper, though he was not violent. If she made a mistake dancing, he would get upset because he thought it made him look bad, she recalled.
Court records indicate Tran filed for divorce in 2005.
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Tran was an immigrant from China, according to documentation on his marriage license shown to CNN.
A former tenant and longtime acquaintance of Tran told ABC News that he was a regular at the dance studios in Monterey Park and Alhambra.
Tran liked to dance, but didn't make friends easily and seemed to be a bit of a loner.
He said Tran "distrusted everyone" and had a personality that displayed paranoia and "hate towards people."
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"I wouldn't say he was aggressive but he just couldn't get along well with people."
He would offer women free lessons at the studio, which didn't endear him to the paid staff.
"Probably, this made the instructors unhappy," he said. "I think there was tension between Tran and those instructors."
The Los Angeles County Sheriff's Department has executed a search warrant for Tran's mobile home in a senior community in Hemet. Records show he previously owned a home in San Gabriel, selling it in 2013 after owning it for more than two decades.
Hemet police say Tran visited the department lobby on Jan. 7 and 9 of this year. He made allegations about fraud, theft and poisoning involving his family in the Los Angeles area 10 to 20 years ago, the department said. He said he would return with documentation proving his allegations but he never showed up again.
Information from ABC News, the Associated Press and CNN was used in this report.