Scene of the Crime

Riddle: A man killed his wife in his car with a knife, and no one could see him. He threw the body out of the car and threw the knife off a cliff. When he got home, the cops called the man and told him his wife was dead and to come to the scene of the crime. The man agreed and rushed to the scene. When he got there, the cops immediately arrested him. Why?

ANSWER: The cops never said where the scene of the crime is.