Old man killed by insane man

A neighbor reported screaming late at night so I, accompanied  by two other police officers, went to the house were the screaming was heard. A man answered the door and said that he was screaming because of a nightmare. He allowed us to look around and after we found nothing let us sit down. The man thought he heard the old man's heart beating and confessed to the crime. This was clear that the man was insane since the old man was dead and therefore his heart was not beating.