The bodies of a man, his mother and a dog were found in a Simi Valley home Thursday night after police responded to a welfare check and found a bomb threat written on a wall of the residence.
Police identified the killer Friday as the woman's son. The man shot his mother and dog before fatally shooting himself, police said.
The shootings occurred while the woman was visiting her son at the house near the 500 block of Fairfield Road, where he lived with an aunt and uncle, police said.
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The man's identity and age were not immediately available.
Early Friday, at least two vehicles were towed from the home in the community about 50 miles northwest of Los Angeles.
Several homes were evacuated and residents were urged to stay away from a house as police and firefighters responded to a call at 6:45 p.m., Cmdr. Steve Shorts, Simi Valley Police Department public information officer, said.
Police found a bloody scene, including the woman's body on the ground floor of the home and a man dead with gunshot wounds. The dog, a husky, was also found shot to death.
Several law enforcement teams responded, including Simi Valley SWAT team and Ventura County bomb squad, after personnel found writing on the wall that indicated the presence of a bomb, but none was found, Shorts said.
The welfare check was called in by a resident of the home. He is alive and accounted for, but the relationship between him and the two dead individuals is unknown, according to Shorts.
Evacuations have been lifted and tactical teams have pulled out, but the investigation is expected to continue until midday Friday. It is not yet known who wrote the bomb threat.