Kroll was a German serial killer and cannibal. He was known as the Ruhr Cannibal (Ruhrkannibale), and the Duisburg Man-Eater (Duisburger Menschenfresser). He was convicted of eight murders but confessed to a total of 13.
Kroll said that he often sliced portions of flesh from his victims to cook and eat them, claiming that he did this to save on his grocery bills. In custody, he believed that he was going to get a simple operation to cure him of his homicidal urges and would then be released from prison. Instead he was charged with eight murders and one attempted murder. In April 1982, after a 151-day trial, he was convicted on all counts and was given nine life sentences.