A 29-year-old Dorchester man is being held without bail this week after he allegedly stabbed his girlfriend to death in a Ridgewood Street apartment on Sunday morning. Luz Forty, 38, was found by police when they were called to the scene. Police say the suspect, Mario Gonzalez, called 911 and told them that an intruder had broken into the apartment they shared and stabbed Luz to death. He later admitted that he was the attacker, according to prosecutors. Gonzalez is due back in court on May 5.