A man murders his wife with a knife in their car. Nobody is around to see this. He throws 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 goes home. An hour later the police call him and tell him that his wife has been murdered and he needs to come to the scene of the crime immediately. As soon as he arrives, he is arrested.
How did they know he did it?
He never ask the cop where the scene of the crime was so they knew that he had murdered his wife.
Why this works
The riddle hinges on the idea of knowledge and awareness. The man, having just committed the crime, should not know where the police would be investigating unless he was involved. When the police called him to come to the scene of the crime, his failure to ask for its location indicated that he already knew where it was, suggesting his guilt. This clever twist plays on the expectation that the man would be confused or surprised about the police's request, but his specific knowledge betrayed him.