Did you see me rob the bank?

A man walks into a bank, gets in line, and when it is his turn he pulls out a gun and robs the bank.

To make sure he leaves no witnesses he turns around and asks the next customer in line, "Did you see me rob this bank?" The customer replies, "Yes," whereupon the robber shoots him in the head and kills him.

The robber quickly moves to the next customers in line a man with his wife and says to the man, "Did you see me rob this bank?"

The man calmly responds, "No, but my wife did."