#2. A Shot In The Dark

#2. A Shot In The Dark:

A man was found dead with a cassette recorder in one hand and a gun in the other. When the police came in, they immediately pressed the play button on the cassette. He said "I have nothing else to live for. I can't go on," then the sound of a gunshot. After listening to the cassette tape, the police knew that it was not a suicide, but a murder. How did they know?

Did you solve the riddle?!