MOSCOW - Russian investigators said Monday they had detained six prison guards over a video showing officers brutally beating an inmate which was leaked to an independent newspaper. The group of prison service employees, "acting deliberately, clearly exceeding their official powers, used violence against a prisoner," investigators said. Human rights activists regularly report torture, humiliation and beatings in Russian prisons, but the leak of such an explicit video is rare. The branch of the Investigative Committee for the Volga city of Yaroslavl, where the video was shot at a penal colony, said "today six people have already been detained."