SF officer suspected of making prohibited assault rifle

A San Francisco police officer was arrested after an investigation revealed he manufactured and possessed a prohibited AR-15 style assault rifle, police said Tuesday.

Thomas Abrahamsen, 50, of Berkeley was booked on suspicion of manufacturing an assault weapon and possessing an assault weapon, both felonies.

In this file photo, Nolan Hammer looks at a gun at the Heckler & Koch booth at the Shooting, Hunting and Outdoor Trade Show in Las Vegas.

In this file photo, Nolan Hammer looks at a gun at the Heckler & Koch booth at the Shooting, Hunting and Outdoor Trade Show in Las Vegas. Photo: John Locher, Associated Press Photo: John Locher, Associated Press Image 1 of / 5 Caption Close SF officer suspected of making prohibited assault rifle 1 / 5 Back to Gallery

An investigation into Abrahamsen began in the summer of 2015 after other members of the department tipped off officials. The probe found the officer manufactured and owned a prohibited assault rifle along with AR-15 receiver components, police said.

Abrahamsen, an 18-year veteran, surrendered Tuesday, authorities said. He was on unpaid administrative leave, police said.

The department’s Internal Affairs Division has given a report on the investigation to the district attorney’s office, police said.

“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 in a statement.

Jenna Lyons is a San Francisco Chronicle staff writer. Email: jlyons@sfchronicle.com

Twitter: @JennaJourno