Shareef Allman, 47, of San Jose allegedly opened fire early Wednesday at an employee meeting at the Lehigh Permanente plant where he worked.
Two co-workers, John Vallejos, 51, and Mark Munoz, 59, died at the scene.
Another, Manuel Pinon, 48, of Newman, died later at a hospital.
Allman also allegedly shot and wounded a Hewlett-Packard contract worker later that morning in an attempt to steal her car.
The wounded were not identified by police.
The shootings have set off a massive manhunt, involving 10 law enforcement agencies, police dogs and helicopters. Officers went door-to-door in parts of Cupertino and the neighboring city of Sunnyvale.
-- Sam Quinones
Photo: Officers search for the suspect in the quarry shooting Wednesday. Credit: Beck Diefenbach / Reuters.