A San Francisco UPS driver who killed three colleagues in a shooting rampage at a company warehouse on June 14 was armed with two stolen guns, police said Friday.
At a news conference, police commander Greg McEachern said investigators have not yet determined Jimmy Lam's motive, but "the shooting appeared purposeful and targeted."
He also reportedly filed a recent grievance citing excessive overtime.
Lam, 38, shot and killed three fellow drivers and wounded two others before killing himself in front of police during the shooting. An 18-year veteran of UPS, Lam opened fire at a morning meeting of UPS drivers before the drivers went out on deliveries.
Benson Louie, 50, was the first victim shot, in the meeting, before Lam turned the gun on Wayne Chan, 56, said McEachern. Lam then walked outside and confronted Mike Lefiti, 46, and fatally shot him multiple times.
According to McEachern, Lam didn't say anything throughout the attack.
Police announced Lam had been armed with two stolen weapons. One was an assault pistol that is illegal in California and was stolen in Utah, which was used in the killings. It was also equipped with a special magazine that held 30 bullets instead of 10 -- gun gear that is illegal in California, McEachern said. Lam also had a semi-automatic handgun stolen from Napa County.
Lam fired a total of 20 shots and didn't use the handgun recovered at the scene. Police found a box of bullets in Lam's backpack. There were metal detectors in the building, but it's unknown how he brought the guns in.
A San Francisco Police Department official told The Associated Press last week that Lam appears to have felt disrespected by co-workers, but it's not clear what role that played in the shooting. A union official familiar with Lam previously said, “I never knew Jimmy to not get along with people.”
"We are going to work painstakingly to try to get a motive," said McEachern. According to police, he had been arrested before for nonviolent crimes.
Friends and colleagues have said that Lam struggled with personal issues and was depressed a few years ago. They said Lam had shown improvement, but he started to look troubled a few weeks ago. That was around the time, in March, when Lam filed a grievance claiming he was working excessive overtime.
Investigators have recovered a journal from Lam's home and are reviewing it, along with seizing multiple phones and computers. McEachern said they have interviewed more than 100 people and are re-interviewing key witnesses.