Otto Warmbier likely died from injuries resulting from oxygen-starvation, but no conclusive evidence of torture was found, an Ohio coroner who examined the U.S. national said on Wednesday.

The results were announced following an interview with Warmbier’s parents on Fox News on Wednesday, in which they said North Korea had “tortured” Warmbier.

Fred and Cindy Warmbier called for North Korea to be listed as a state sponsor of terrorism, in their first joint interview since their son died in June this year.

“We don’t know what happened to him and that’s the bottom line,” the coroner for Hamilton