SAN FRANCISCO (KTVU) -- The UPS worker who opened fire at the company's San Francisco warehouse yesterday, killing three co-workers before turning the gun on himself believe he was being bullied by two of those employees, sources told KTVU Thursday.
Jimmy Lam, an 18-year veteran of UPS, appeared to single out three slain drivers during the shooting rampage although police have not yet publicly disclosed a motive in the case. San Francisco police declined to comment about their investigation on Thursday.
One of the workers that Lam targeted was Benson Louie, 50, who was shot and killed after a morning meeting with staff. A second employee whom Lam thought was mistreating him was not at work during the shooting attack.
Sources said Louie was the first victim and he was shot in the head before he died at the scene.
The two other victims, Mike Lefiti, 46, and Wayne Chan, 56, a 28-year UPS veteran also died during the attack. Sources told KTVU that Lam had not had any problems with Lefiti and Chan so it remains unclear why those two were shot.
Inspectors have interviewed more than 150 witnesses.
Friends and colleagues recounted several personal and professional troubles that Lam had been experiencing.
Most recently, he was upset with UPS managers and had filed a grievance in March claiming he was working excessive overtime, said Joseph Cilia, Lam's friend and an official with the union that represents UPS drivers. But none of the men who were shot were managers, Cilia noted, adding that he knew of no disputes between Lam and the victims.
Shaun Vu, a senior UPS driver, said Lam had personal troubles a few years ago that involved a dispute with a girlfriend over visitation rights for their young child. Vu said he encouraged Lam to seek professional help and that Lam took off work for several months.
Lam seemed fine when he returned to work but Vu noticed a few weeks ago that he looked troubled.
"I just saw him passing by and asked how he was doing," Vu said. "He said something like, `I'm hanging in there.' "I don't think he had anybody he could talk to and it got worse and worse."
Lam had a run-in with the law in 2010, when he was convicted in San Francisco of driving under the influence and sentenced to three years' probation.
Lam was a U.S. citizen who emigrated to the United States as a baby from Thailand, said Sharon Rummery, a spokeswoman for U.S. Immigration and Citizenship Services. She declined further comment.
As UPS workers returned to the scene of the shooting one day after gunfire erupted at the warehouse facility in San Francisco's Potrero Hill neighborhood.
About 20 people brought flowers, a signed volleyball and T-shirt for Louie, their former volleyball coach. Many were sobbing and hugging each other.
"The biggest thing was just the size of his heart," said Darrick Ly, who met Louie when he was only 14 years old. "He was always there for us anytime we needed anything, whether we were hungry and he wanted to give us some chicken wings and we were there, but even if he needed a hug and shared a story to help us get through the day."
"It's rough for us ... seeing people you work with and then they're gone," said UPS worker Joshua Watson.
"That's where Mike- he would come through that door," said Isaiah Miggins, pointing. "He'd laugh and say hi to everybody and so I'm used to seeing him every morning."
Miggins said he talked to Lefit in the coffee shop earlier that morning and left the UPS facility on 17th and Utah streets just five minutes before the shooting started.
"Everyone's real emotional right now," Miggins said. "It's sad."
Workers who played volleyball with Louie called him "Uncle Benson." They don't understand why Lam or anyone would want to hurt the married father of two girls.
"We're all baffled," Ly said. "We're all trying to figure this thing out. We're just taking it one day at a time."
UPS offered grief counseling to employees and said the company was working to help everyone heal while also trying to understand what led up to the tragedy.
UPS spokeswoman Susan Rosenberg said the company has marshaled additional drivers, loaders and management from other facilities to help with the backlog. Grief counselors were also at the facility.
UPS CEO David Abney said the company was investigating the circumstances that led to the shooting.
Isaiah Miggins, a UPS loader on the overnight shift, said it was hard to finish his shift.
"Everybody was down," Miggins said, adding that UPS is like the U.S. Post Office: "We gotta get those packages out."
KTVU reporter Tara Moriarty and the Associated Press contributed to this report.