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"Information was obtained that a 3-year-old female was not breathing and her face was turning blue," the department said in a Facebook post. "Upon arrival of officers, life-saving measures were taken until paramedics arrived on scene transporting the victim to a local hospital."
The girl died Sunday, police said.
Montano, initially charged with attempted murder, is now facing a murder charge, police said. According to KABC-TV, she previously pleaded no contest to child abuse charges in 2015 and was still on probation.
Rojo was charged with felony child endangerment.
The Department of Children and Family Services now has custody of two other children who lived in the home, authorities said.
>> See the Police Department's Facebook post here