SAN FRANCISCO (AP) — A transit police detective who shot and killed a fellow officer in January accidentally mistook him for an armed assailant and won’t be charged, California prosecutors said in a report released on Friday.Bay Area Rapid Transit Detective Michael Maes shot BART police Sgt. Tom Smith on Jan. 21 as the two searched an apartment in Dublin for stolen items.Alameda County deputy district attorney John Creighton wrote in the report that Maes fired once after he saw a shadowy figure with an upraised firearm suddenly come out of a dark walk-in closet area. Creighton said Smith’s upraised arm could have obscured the identifying police markings on the front of his bullet-proof vest.“His decision to discharge his weapon was an objectively reasonable response to his perceived threat,” Creighton concluded. Maes participated with the investigation, Creighton said.Smith, 42, was a 23-year veteran of the BART police force and Maes’ supervisor.