Jeffrey Edmonds, 37, was arrested on Tuesday outside of his home. Neighbors were stunned when officers swarmed the house.
"We didn't know him, so we never knew what was going on. But he was nice," said neighbor Esther Ringo.
The sheriff's department says earlier this month a firearms manufacturer in Castaic reported that two upper receivers used to build AR-15 assault rifles had been stolen. Authorities identified Edmonds as a suspect.
"The suspect possessed a counterfeit LAPD captain's badge and ID card and was using that to impersonate himself as a sworn peace officer," said Deputy Joshua Dubin with the Los Angeles County Sheriff's Department.
Investigators say they recovered the stolen receivers from the house along with bulletproof vests, ballistic helmets, grenades and other tactical equipment.
"We have no indication at this time that the suspect had foul intentions with the stockpile of weapons. However, we are still tracing back to the owners of the weapons if any of the weapons were stolen," said Dubin.
Edmonds was booked at Santa Clarita Valley Station on charges relating to grand theft, impersonating a peace officer and weapons violations. His bail was set at $250,000. He is expected to appear in court on Thursday.