A man murders his wife with a knife in their car which no one is around to see. He rolls her out of the car being careful not to leave any fingerprints on her body. Next he throws the knife off of a cliff into a gorge where it will never be found and he heads home. An hour later the police call him and tell him that his wife has been murdered and he needs to come to the crime scene immediately. As soon as he arrives he is arrested.
Why was he arrested?