A man cut off his own head with a chainsaw after stabbing his 70-year-old father to death in their apartment in the German city of Cologne, police said.

The body of the offender, 24, was found headless when police raced to the apartment after an emergency call, apparently from the dying father, had been broken off in mid-sentence.

Alf Willwacher, a senior prosecutor, said an electric chainsaw was next to the son's body.