SAN FRANCISCO (CBS SF) — A San Francisco police officer was arrested Tuesday for allegedly manufacturing and possessing an AR-15 style assault rifle and prohibited parts, following a year-long investigation by the department’s Internal Affairs Division.

The officer, identified as 50-year-old Berkeley resident Thomas Abrahamsen, surrendered himself and was booked into San Francisco County Jail on one felony count of manufacturing an assault weapon and one felony count of possession of an assault weapon, according to a statement released Tuesday night by San Francisco police spokesman Sgt. Michael Andraychak.

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Abrahamsen, an 18-year veteran of the police department, has been placed on unpaid administrative leave, according to Andraychak.

His arrest stems from an investigation that was opened in the summer of 2015 and was apparently based on information gathered from his colleagues.

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Along with the announcement of Abrahamsen’s arrest, the police department has stressed the importance of the public’s trust to the members of the department, and said they would work hard to build and maintain that trust.

In the statement released Tuesday night, San Francisco’s Acting Chief of Police Toney Chaplin said, “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.”

The police department states that its Internal Affairs Division has provided the completed investigation to the San Francisco District Attorney’s Office and that Abrahamsen’s booking photo is expected to be released to the public on Wednesday.

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By Hannah Albarazi – Follow her on Twitter: @hannahalbarazi.