A delivery truck driver gunned down three of his co-workers at a United Parcel Service (UPS) facility in San Francisco, California Wednesday morning local time.

The attack ended when the gunman identified as Jimmy Lam, a San Francisco resident, shot and killed himself.  

According to San Francisco police, two people wounded in the shooting were sent to the hospital for treatment. Five others suffered minor injuries.

Authorities said the attack is not being treated as an act of terror, but the motive is still under investigation.