But it's not clear how the three girls, who ranged in age from 3 years to 2 months old, were killed, Los Angeles County sheriff's Lt Dave Coleman said.
Detectives were completing their investigation and clearing out of the scene this morning, more than 12 hours after the suspect's mother called them to the home in the unincorporated area near Torrance.
Neighbours say the mother, identified by authorities as 30-year-old Carol Coronado, was taken from the scene covered in blood and naked except for a blanket.
"She was full of blood on her face and arms," neighbor Ashley Madrid told the Daily Breeze newspaper.
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Coronado was arrested yesterday on suspicion of murder, taken to a hospital for examination and then to a sheriff's station for booking. Authorities say she made no statement.
Madrid said the children's grandmother told her that the woman had called earlier in the day and said that she was going crazy. She said the children's father was working on his car across the street when his mother-in-law discovered her daughter and the three children in a pool of blood on a bed.