The Punta Gorda policeman who tragically shot and killed a retired librarian when he fired real bullets — instead of blanks — at her during a citizens academy is a former Miramar officer with a troubled record, forced to resign from his job at the end of his rookie year. Three years before the shooting that led to the death of 73-year-old Mary Knowlton on Tuesday, Lee Coel was accused twice of using excessive force and relieved of his duties before investigators found he violated department policies and was allowed to resign. This year, he was sued in Punta Gorda after he ordered his K-9 to attack a bicyclist who was stopped for riding without a light at night, inflicting severe injuries that required surgery. The officer’s background provides yet another twist to the death of the woman who was shot during a role-playing session in which she was a crime victim and he took the part of the “bad guy,”