The suspect was allegedly wearing a mask when he entered the bank and demanded money from the teller. He then threatened to detonate a device that was inside a white box, according to police.
Police said the suspect later exited the building and was holding the white box containing stolen money and the suspicious device. At that point, police opened fire.
"Due to the threat of a possible explosive device, the Orange County Sheriff's Department Bomb Squad responded to render the suspicious devices as well as the crime scene safe," police said in a news release.
The suspect had what police said called a facsimile device at the time of the shooting, said Kristy Wells, a Fullerton Police Department spokeswoman. He was pronounced dead at the scene.