San Francisco police officer Thomas Abrahamsen pleaded not guilty to two felony weapons charges.  (Photo: LA Times)

An 18-year veteran of the San Francisco police department has been charged with two felony weapons charges for building and possessing a prohibited AR-15, officials announced Wednesday.

Officer Thomas Abrahamsen surrendered to authorities earlier this week and yesterday pleaded not guilty to both charges.

Abrahamsen was arrested after a year-long investigation by the department’s Internal Affairs division, which began looking into Abrahamsen after receiving a tip from a fellow officer.

“In the spirit of the Not on My Watch initiative, Department members will continue to hold each other accountable and will act swiftly to report any behavior that might bring dishonor to the Police Department,” acting Police Chief Toney Chaplin said.

The initiative Chaplin references was instituted in the wake of a scandal in which dozens of officers were found to have exchanged text messages with anti-gay and racist content.

“He has some significant health issues. We’re really pleased he was released today and he looks forward to dealing with the case and explain exactly what’s going on,” Defense Attorney Michael Hinckley told ABC 7. “A curious part of this case is the fact that Abrahamsen was apparently turned in by his fellow cops. Acting chief Tony Chaplin says it’s evidence that his internal reforms are working.”

It isn’t yet clear how Abrahamsen’s firearm violated California law. Considering the fact that the department has been investigating Abrahamsen since last summer, the violation likely does not stem from the new gun control measures signed by California Gov. Jerry Brown.

But according to the LA Times, Abrahamsen was charged under a state law that prohibits assembling a rifle capable of firing a .50-caliber BMG bullet or, as of July 1, possessing an AR-15 with a “bullet button.” If Abrahamsen’s firearm was equipped with a bullet button, he should be allowed to keep it since he possessed it before the new law came into effect.

If he built a .50 BMG AR-15, he’ll be in some hot water.

“The gun was not a duty firearm and it had nothing to do with his employment at the San Francisco police department,” San Francisco District Attorney Office spokesperson Alex Bastian said. Police officers are allowed to have modified AR-15’s with written permission from their department, but, according to the ABC 7 report, it appears that Abrahamsen did not have permission.

Abrahamsen has been released from jail provided he turns over all his firearms. He is scheduled to appear in court again on August 12.