This guy raped and killed a pregnant newlywed woman. He was executed and it took longer than usual. I would say however he died is probably less painful than being raped and stabbed to death.
http://www.wistv.com/story/24467184/lawyer-says-ohio-killers-execution-was-botched
http://www.wistv.com/story/24467184/lawyer-says-ohio-killers-execution-was-botched