SAN FRANCISCO (KRON) — There is a number of questions Thursday about why one UPS employee would open fire killing three others.

San Francisco police are remaining quiet about a motive, while those who knew the victims are trying to make sense of it all.

One day after a UPS employee shot and killed three co-workers before killing himself at UPS’s San Bruno Avenue customer center in San Francisco, those who knew the drivers are looking for answers.

“It’s senseless,” Teamsters Local 2785 Secretary Treasurer Joseph Cilia said. “It’s the only word that keeps coming to mind from the minute I heard–to disbelief to know why.”

Cilia knew all three victims and the shooter Jimmy Lam.

“They all worked with each other for many years,” Cilia said. “We had no knowledge of issues.”

Cilia says Lam filed a request back in March to reduce his overtime hours and believes that was resolved immediately because it never escalated to a formal grievance.

“It’s senseless–all family men, Father’s Day coming up, they all had families,” Cilia said. “Jimmy had a family as well.”

As UPS drivers returned to their routes on Thursday, a memorial for victim Mike Lefiti, known as Big Mike, continued to grow at the Diamond Heights Shopping Center.

“He was a piece of sunshine,” said Susan Wasserman, who lives on Lefiti’s route. “He used to tell me he loved when we got packages because it meant he had an opportunity to come say hello, and he was just a sweetheart.”

In the Sunset District at Harvest Books and Gifts, owner Margaret Lee is remembering another victim, Benson Louie, who used to pick up and deliver to her store.

“That’s the kind of guy he was, always give you a helping hand and just a great guy,” Lee said. “I’m going to miss him.”

UPS has issued the following statement on Thursday:

UPS has trained grief counselors onsite and have directed employees to confidential resources through our Employee Assistance Program. I know there were 14 counselors at the building today. Yesterday, there were social workers and clergy present, but I’m not sure how many. The assistance becomes focused to the needs of the individual for ongoing support. Our management team also has been in touch with family members of our deceased drivers and our two drivers who were injured.

Operations resumed out of the building today. We already had contingencies in place because of the Golden State Warriors NBA victory parade and corresponding street closures.

UPS marshaled additional drivers, pre-loaders and management from other area facilities for assistance with our service recovery that will continue through Friday. Tracking systems have been updated on ups.com to reflect new delivery information.

It wouldn’t be unusual to have additional driver helpers on vehicles (a common practice during the busy holiday period) as a way to complete the heavier volume of deliveries and pickups today and tomorrow to catch up for the service impacts related to the halt to service on Wednesday.

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