[5] The shooting happened at about 10:22 p.m. PST (UTC-8) at Star Ballroom Dance Studio, after an all-day Lunar New Year Festival was held on a nearby street.

Monterey Park police responded within three minutes of the first 9-1-1 call, finding "individuals pouring out of the location screaming" when they arrived.

As officers approached the van, they heard a single gunshot coming from inside, retreated, and requested tactical units to respond.

[43] During the standoff SWAT officers, both visually from their armored vehicles and via a drone-mounted camera, observed the man in the driver's seat slumped over the steering wheel of the van.

[32][47][48][49][50][51] An eleventh victim, Diana Man Ling Tom [note 9], 70, died at the LAC+USC Medical Center the day after the attack; she was from Hong Kong.

[31][56] According to different documents, he was reportedly from China[57] or Vietnam;[24][58][59] police stated that Tran was of Vietnamese origin, but had also lived in Hong Kong in the past.

[61] Tran eventually immigrated to the United States, working various jobs, including truck driving and carpet cleaning, residing in Texas for several years before moving to San Gabriel, California in August 1989.

[31] In 2020, Tran bought a double-wide trailer in a senior community at a mobile home park in Hemet,[5][62] a suburb about 85 miles (137 km) east of Los Angeles.

The earliest recorded instance was on December 26, 1992, when Tran called police to his address about being threatened, later telling the arriving officer that the husband of his girlfriend, who were in the middle of a divorce, had connections to a "Taiwanese gang" and was trying to kill him.

Three weeks later in January 1993, Tran reported that he found 49 shotgun shells on his front lawn which he believed were meant as a threat against his life, but did not request help, reasoning that he called "only to make the police department aware of the situation in case something happened".

Tran made similar claims later in 1999, saying that he had been consistenly receiving calls for nine months, with the person on the other end remaining silent whenever he picked up the phone.

An earlier attempt made by police to tap his phone with a recording device at Tran's request failed due to a "malfunction" shortly after installation.

[56][18] Law enforcement found a Savage Arms .308 caliber bolt-action rifle,[56][18][21][22] hundreds of rounds of ammunition,[56][10] and items suggesting that Tran was manufacturing suppressors.

[66][67] During the manhunt for the gunman, President Joe Biden instructed the Federal Bureau of Investigation to provide full support to the local authorities.

[68] Los Angeles Mayor Karen Bass called the shooting "absolutely devastating", and Governor Gavin Newsom said that he was "monitoring the situation closely".

[6] Security preparations were stepped up ahead of Lunar New Year celebrations in New York City, Miami, and Los Angeles.

[73] Moments of silence across the country were held at Lunar New Year festivities as well as sporting events involving teams from Los Angeles.

[74][75] It became the deadliest mass shooting in the history of Los Angeles County, exceeding the death toll of a massacre in Covina in 2008.