A man walked in the house. He was about to hang up his coat when he heard his wife say, "No John! Don't do it!" There was a shot and the woman was dead. There was a police officer, a doctor, and a lawyer standing next to her. The woman's husband knew that the police officer did it. But how did the husband know?
The police officer was a man while the doctor and lawyer were ladies. John is a man's name. The husband's name was David. So John was the police officer's name. David's wife was saying, "No John! Don't do it!" to the police officer and the police officer shot her anyway.