ETNA GREEN, Ind. (AP) — Preliminary autopsy results indicate three teenagers found dead in a car in northern Indiana might have died from carbon monoxide poisoning, Indiana State Police said Monday.

The teens were found unresponsive Sunday in the car on a rural property near the Kosciusko County town of Etna Green, about 30 miles (48 kilometers) southeast of South Bend, police said.

Preliminary indicators from autopsies performed Monday at the Northeast Indiana Forensic Center in Fort Wayne point toward carbon monoxide poisoning as the cause of death but toxicology results are pending, police said.

Robert Bontrager, 18, of Rome City was sitting in the driver’s seat and two Topeka 16-year-olds, Karen Miller and Nathan Yoder, were in the back seat, police said. All three teenagers were pronounced dead at the scene.