A man who was shot to death Sunday night in the South End has been identified as Mohamed Hassan, 21, of Boston, the Police Department said. Police responded to a call at approximately 9:30 p.m. for a person shot near 423 Shawmut Ave. Police found Hassan, who had sustained a gunshot wound. He was pronounced dead at the scene. Anyone with information is asked to call detectives at 617-343-4470. Those who would like to leave an anonymous tip may call the CrimeStoppers Tip Line at 800-494-TIPS or by texting the word TIP to CRIME (27463).