BROOKLYN, Iowa — The Iowa college student who was allegedly abducted by a stranger while running last month in a small Iowa town was killed by “multiple sharp force injuries,” investigators announced Thursday.

Preliminary autopsy results from the state medical examiner’s office also determined that 20-year-old Mollie Tibbetts was the victim of a homicide, the Division of Criminal Investigation announced in a press release.

The agency did not release additional details about the injuries Tibbetts suffered or what caused them, but said further examination of her body may result in additional findings. Autopsy reports are confidential under Iowa law, except for the cause and manner of death.

The man charged with first-degree murder in Tibbetts’ death, Cristhian Bahena Rivera, allegedly led investigators to her body early Tuesday in a cornfield outside of Brooklyn, Iowa, the town where she was last seen last month. While investigators were confident then that the body was that of Tibbetts, the autopsy definitively confirmed her identity.

Prosecutors allege that Rivera abducted Tibbetts while she was out for an evening run in Brooklyn on July 18, killed her and disposed of her body in the secluded location.

A criminal complaint alleges that Rivera confessed during a lengthy interrogation that began Monday to following Tibbetts in his car, getting out on foot and chasing after her. Rivera told investigators that he panicked after Tibbetts threatened to call police on her cell phone, he blacked out and later came to when he was unloading her bloody body from the trunk of a car, it says.

Rivera worked for the last four years at a dairy farm a few miles from where Tibbetts was last seen. He and Tibbetts have no known connections, other than that Rivera allegedly told investigators that he saw her running previously. Investigators zeroed in on him as the suspect after obtaining footage from surveillance cameras showing a vehicle connected to him circling the area of Tibbetts’ running route.

Earlier this week, investigators said they were uncertain how Tibbetts was killed or whether she was sexually assaulted. They’ve made no mention of recovering a weapon linked to the death.

Rivera, a native of Mexico who is suspected of being in the U.S. illegally, made his initial court appearance Wednesday and is being jailed on a $5 million cash-only bond. He faces life in prison without the possibility of parole if convicted.