Iowa college student Mollie Tibbetts was killed by “multiple sharp force injuries,” according to a preliminary autopsy on Thursday that also confirmed the body found in a field Tuesday was Tibbetts.

Tibetts’ death has been ruled a homicide, and the state medical examiner has not shared any information about what kinds of object could have caused the injuries, reported The Associated Press. A stab wound is an example of a sharp force injury.

Her accused killer, Christian Bahena Rivera, said he put Tibbetts, who was bleeding, in the trunk of his black sedan and left her body in a cornfield near rural Brooklyn, Iowa, according to an affidavit, reported CNN.

Rivera, a 24-year-old illegal alien, was charged with murder Tuesday. He has resided in the area for four to seven years, officials said. He led investigators to the body’s location after confirming that he interacted with her while she was running. Tibbetts felt threatened by him and said she would call 911 on him, according to reports.

Rivera said he “blacked out” at some point during their interaction, officials said. (RELATED: Illegal Immigrant Charged With Murder Of Iowa College Student Mollie Tibbetts)

Tibbetts was last seen alive on July 18.

The young woman was a rising sophomore studying psychology at the University of Iowa in Iowa City. She enjoyed reading and public speaking and was a member of the Catholic Church, reported the Des Moines Register.

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