The suspect's grandmother survived the stabbing, but his mother did not. Police officers said they opened fire when the suspect came at them with the knives.
The incident started as some kind of argument between Hector Hernandez, 36, his mother and his grandmother, according to authorities. Somehow that argument escalated into a fatal stabbing.
"When the body came out, you could tell that he just slit her throat," said neighbor Dusty Garcia.
Garcia lives across the street from the crime scene on the 1500 block of Arapahoe Street. He said he heard an elderly woman crying for help, saying her grandson was armed with two knives.
"I asked her if she was OK, and she said she was OK and to go check on her daughter. She felt that [her daughter] was dying or dead," said Garcia.
When police arrived at around 1 p.m. Monday, the 85-year-old grandmother told them her grandson was responsible for the attack and that her 60-year-old daughter was still inside.
Four police officers responded and found Hernandez in the backyard.
"The suspect screamed at the officers and charged them, and an officer-involved shooting occurred," said Los Angeles Police Department Sgt. Mitzi Grasso.
It's unclear how many times Hernandez was shot. Investigators said Hernandez slashed his own throat before confronting police.
Officials said the suspect had no history of mental illness and no criminal history.
The incident remained under investigation.