South Pasadena police officers responded shortly before 10 a.m. to a report of a domestic violence incident in progress in the 500 block of Five Oaks Drive, according to the Los Angeles County Sheriff's Department.
The officers arrived to find one of the home's front windows shattered and heard women screaming inside, a news release said. Police entered the residence and discovered a man in his 40s who had been gravely injured.
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Firefighter-paramedics arrived at the scene and pronounced the man dead. He was later identified as Justin Goss, 40, of Glendale.
According to sheriff's homicide detectives, an investigation indicated that while the intruder "was in the process of beating and choking the female victim, her mother and sister came to her aid. During the struggle, the suspect was stabbed and beaten with a golf club."
The man's estranged girlfriend was taken to a hospital and treated for facial injuries, authorities said. She was later released from the medical facility.
Anyone with information about the incident is urged to call the sheriff's Homicide Bureau at (323) 890-5500.