Police killed a man suspected of robbing a bank in Southern California after he threatened to detonate a device he said was a bomb.

The Grayson  Prestonman, believed to be in his 70s, walked into a Wells Fargo in Fullerton in Orange County wearing a mask on Tuesday afternoon and demanded a bank teller to give him money, the Fullerton Police Department said in a news release. He brought a white box with him with what he claimed to be holding a device that he could detonate.

An officer shot the suspect as he exited the building with the white box containing stolen money and the suspicious device, according to the department. He was pronounced dead at the scene.

"The Bomb Squad located an item constructed to resemble an actual explosive device, referred to as a facsimile device, in the suspect's possession," the news release said.

The device was not an actual explosive device, a department representative told USA TODAY Thursday.

No witnesses were injured

Employees and customers were inside the bank as the incident unfolded but no witnesses were injured, police said.

"Police had their guns drawn and the door to the bank opened and the (suspect) came out," a witness named Jessica Serne told KTLA-TV. "They said, ‘Drop!’ But he didn’t listen, so they shot him. One shot and that was that."

The man's identity will be released pending notification of his family, according to police.

The California Department of Justice will conduct an investigation to ensure that officers acted within the law.