A college student who collapsed at her professor's Phoenix home died of a cocaine overdose, an autopsy concluded.

Paradise Valley Community College student Andria Ziegler, 19, died April 20 after being taken from psychology professor Michael Todd's home to a hospital.

Todd, 51, is in the process of being fired from his job for allegedly violating college district policies prohibiting instructors from having romantic relationships with students.

The Maricopa County Medical Examiner released the results of the autopsy on Wednesday, and concluded the death was due to an accidental cocaine overdose. No alcohol was in her system, despite a recording of Todd's 911 call seeking help where he said they had been drinking and Ziegler had been doing cocaine.

Phoenix police are investigating the case as an unknown death and have not labeled it as criminal in nature.

Ziegler's stepfather, Doug McManus, told the East Valley Tribune on Wednesday although her family figured her death would be drug-related, but that there are still unanswered questions.

"She was 19 years old and healthy when she went to his home," McManus said. "It's the circumstances surrounding her death we are suspicious about."

Todd's lawyer, Michael Roth, released a statement soon after Ziegler's death expressing condolences to Ziegler's family from Todd. Roth has not responded to other requests for comment.