June 23 (Reuters) - The UPS employee who shot three coworkers to death last week inside a United Parcel Service facility in San Francisco before killing himself appears to have singled out his victims deliberately, but a motive remains unknown, police said on Friday.
Investigators have yet to examine the contents of computers, cell phones and a journal seized from the gunman's home in their search for clues to the June 14 attack, San Francisco Police Commander Greg McEachern said at a news conference.
McEachern also revealed the murder weapon was a MasterPiece Arms "assault-type pistol" that he said was "commonly known as a MAC-10," equipped with an extended 30-round magazine. He said such weapons are outlawed in California.
That gun and a second, semiautomatic pistol recovered from the scene were both listed as stolen weapons - the MAC-10 from Utah and the other handgun in California, McEachern said.
Police offered few new details about how the shooting itself unfolded.
The gunman, Jimmy Lam, 38, was attending a morning briefing with fellow employees at the UPS package-sorting and delivery center in San Francisco when he pulled out a gun and "without warning or saying anything" opened fire on four co-workers, the police commander said.
The first two victims, identified as Wayne Chan, 56, and Benson Louie, 50, were killed.
In the ensuing pandemonium, Lam walked calmly outside the building, approached another co-worker, Michael Lefiti, 46, and shot him dead without uttering a word, then reentered the facility.
Moments later, as police closed in, Lam put a gun to his head and pulled the trigger, McEachern said, adding that Lam fired about 20 rounds in all before the bloodshed ended. Police never fired a shot.
While no motive has been established, McEachern said interviews of various witnesses have led investigators to believe that the three slayings were "purposeful and targeted," based on actions observed that day.
He said surveillance video also showed that during the rampage, Lam appeared to pass by other co-workers "without there being any interactions," suggesting those he did shoot were intentionally singled out. It was less clear whether the two surviving gunshot victims were deliberately targeted, he said.
News of the carnage in San Francisco was largely overshadowed that day by an unrelated shooting hours earlier in the Virginia suburbs of Washington that left a congressman and several others wounded before police killed the assailant. (Reporting by Steve Gorman in Los Angeles; Editing by Bill Rigby)