A Los Angeles woman who decapitated her 4-year-old with a kitchen knife showed signs of mental illness nine months before the attack, yet Los Angeles County child welfare officials decided she wasn't a serious threat to the boy.

Lars Sanchez was found dead on July 18 in a bedroom he shared with his mother.

The Los Angeles Times reported Tuesday that nine months earlier, Yolanda Tijerina was seen screaming and shouting "I think you killed my son" outside the boy's Highland Park preschool.

The principal called a child abuse hot line.

Child welfare and mental health officials investigated but the boy wasn't removed from his home. Authorities concluded that any risk could be addressed through informal monitoring by relatives and neighbors.