OAKLAND — A security guard was arrested and charged with illegal gun possession in a case that started when the Alameda County Sheriff’s Office discovered he’d forged a permit to carry a concealed handgun, court records show.

The 38-year-old Berkeley man was charged with possessing an assault rifle allegedly found at his apartment, and with unlawful firearm activity. He pleaded not guilty on Oct. 24 and remains out of jail.

Police say the investigation started when the defendant’s former employer, a Bay Area security firm, called the sheriff’s office to verify his concealed carry permit and found he’d forged it. The permit had been ostensibly issued by Sheriff Yesenia Sanchez. He was fired after this was discovered, authorities said.

Investigators followed up by searching the man’s apartment, where they found an unserialized short-barreled AR-15 rifle, according to court records. The man allegedly told police he was the restrained party in a domestic violence court order, which means he shouldn’t have had the gun even if it had been serialized, authorities say.

A replica Glock pistol and 19 fentanyl pills were also found in his car, according to police.