Investigators still don't know what drove gunman Jimmy Lam to kill his coworkers June 14, San Francisco Police Cmdr. Greg McEachern said at a news conference Friday afternoon. The victims — Benson Louie, Wayne Chan and Michael Lefiti — died at the scene.
But evidence, including interviews with hundreds of witnesses, indicated the shooting was "purposeful and targeted," McEachern said.
"We are going to work painstakingly to try and get to a motive," he said. "At this time, I can't say whether we will or not be able to reach that point."
The gunfire began about 8:50 a.m. at an employee meeting, where Lam and the victims were in attendance.
During the meeting, the commander said, Lam pulled out an assault-style pistol with an extended magazine and "without warning or saying anything" he shot Louie, 50.
After shooting Louie, Lam shot Chan, 56. Two other workers who were shot survived their injuries, McEachern said.
The shooting triggered panic among employees who ran toward the exits of the San Bruno Avenue package center.
Lam, 38, was seen in a surveillance video "calmly walking outside the building," McEachern said.
Lam then walked up to UPS driver Lefiti, 46, who was standing at San Bruno Avenue and 17th Street.
"Without speaking to him, Mr. Lam shot Mr. Lefiti multiple times," the commander said.
Lam then reentered the building.
The first arriving officers, who were equipped with body cameras, entered the building and began searching for Lam. As they combed the building, officers found several employees hiding and others trying to run away.
Minutes later, officers found Lam who had a firearm pointed to his head, McEachern said.
As they instructed Lam to put down his gun, he shot himself, the commander said.
Lam fired a total of 20 rounds during the shooting, McEachern said.
At the scene, investigators recovered Lam's backpack, which contained a box of ammunition as well as two stolen firearms — a semiautomatic pistol from Napa and the MAC 10 with a 30-round magazine from Utah.
Authorities said Lam, a San Francisco resident, used the MAC 10 in the killings.
Detectives are reviewing a journal, cellphones and computers taken from Lam's home.
"We haven't located anything beyond that journal or information that provides clarity to a motive in this incident," McEachern said.
During the shooting, McEachern said, Lam walked past several employees and didn't open fire on them. He said "that would lead us to believe these specific individuals were targeted."
A Teamsters Union official told the Associated Press that Lam had filed a grievance in March complaining about excessive overtime. The Teamsters local represents UPS workers in San Francisco.
The union official said the gunman seemed to have targeted the three drivers who were fatally wounded.
Investigators are still trying to determine if the surviving victims were targeted, he said.
Lefiti, a Hercules resident, had been with the parcel service for 17 years. Lefiti is survived by a wife and five children.
Louie was a San Francisco native who coached volleyball and was called "Uncle Benson" by several of the people he coached. He leaves behind a wife and two daughters.
Chan had been with the delivery service for 28 years.
The building where the shooting occurred processes packages for delivery in the San Francisco area. The facility employs about 350 people.
Chief William Scott said officers at the police academy had come to know some of the facility's employees through the course of their delivery work.
"Anytime you have an incident of this magnitude, it's traumatizing," Scott said at the news conference. "It's traumatizing to the people involved and it's traumatizing those of us in this city that had experienced this unfortunate incident."