A gunman opened fire on his fellow employees at a UPS facility in San Francisco, killing three people before turning the gun on himself. The shooting occurred just before 9 a.m. local time on Wednesday.

"We cannot provide information as to the identity of persons involved at this time, pending the police investigation," UPS spokesperson Steve Gaut told reporters. "The company is saddened and deeply concerned about affected employees, family members and the community we share. Our thoughts and prayers are with all those touched by this incident."

The victims' names are being withheld until their families have been notified. Other employees at the site referred to the shooter as "Big Mike." Police have not yet discovered the gunman's motive.

Assistant Police Chief Tony Chaplin announced that, in addition to the three dead workers, two others were shot but survived. The investigation is just beginning, but at this time there is only the one suspect.

"Our investigators are going through, painstakingly interviewing with everyone that was in the building when this tragedy occurred," Chaplin said.

The situation is now secure, and a press briefing has been scheduled for 2 p.m. (5 p.m. ET).

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