Authorities are still searching for the suspect in Thursday's armed robbery in Copperopolis.
New details emerged Friday when the Calaveras County Sheriff's Office reported that the heist also included a bomb scare.
The robbery was reported around 2:30 p.m. at Firefall Jewelers on Stone Street.
A store clerk told the Sheriff's Office and Angels Camp Police Department that a man walked into the store with a round object, which he described as a hand grenade, and said he had an accomplice standing on the roof with a "high-powered rifle."
He also said he was going to leave a package behind the building, indicating it possibly contained an explosive device, according to the Sheriff's Office.
The man stole a "significant amount" of jewelry and fled the scene, possibly in a teal or dark green Ford Ranger, the Sheriff's Office said.
A witness told investigators that a man matching the suspect's description placed a package on the ground behind the building.
The Calaveras County Bomb Squad responded and determined the package did not contain an explosive.
Authorities are looking for a man described as about 5 feet, 10 inches tall, with brown hair, a medium build and bruised eye. He was last seen wearing a red hat and black sweat jacket.
The Sheriff's Office did not have a sketch available on Friday.