PHOENIX -- A Valley mother is under arrest after she fell asleep on her couch and smothered her 7-month-old boy, Phoenix police said.

Phoenix Fire Department crews responded to a 911 call regarding a baby who wasn't breathing, Phoenix police Officer Jonathan Howard said.

The baby was taken to a nearby hospital where he was pronounced dead, Howard said.

The baby's mother, Elizabeth Ortiz, 30, fled as crews tried to help the baby, and police officers later discovered she had an outstanding arrest warrant, Howard said.

She later returned to the home and spoke to investigators, and she admitted to using drugs, Howard said. Officers said they think the drug use might have caused her to accidentally smother the child.

Howard said investigators are waiting for the results of toxicology reports and the autopsy.

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Ortiz was arrested on suspicion of child abuse and the outstanding felony warrant.