Woman Allegedly Stabs Mother to Death at Assisted Living Facility in Covina

Police said Machiko's 43-year-old daughter, Athina Sumi Rivera, was spending the night in her mother's room at the location.

Police on Monday were trying to figure out why a daughter stabbed her 61-year-old mother to death in an assisted living facility in Covina.

The woman, identified by police as Athina Sumi Rivera, 43, had been spending the night in her mother's room when police responded to a call of an unresponsive woman in the 800 block of West San Bernardino Road just after 5 a.m.

When officers arrived, they found the victim lying on the floor of her room with multiple stab wounds.

She was identified as Margaret Machiko Yamaguchi.

Rivera was booked into jail on suspicion of murder. Her bail was set at $1 million.

Police said residents of these types of facilities are allowed to have guests. They are like studio apartments for those who need help.

It's unclear why Yamaguchi needed the assistance, but her daughter was spending time with her since Friday, staying in the room overnight.

Mekahlo Medina contributed to this report.

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