Answer this RIDDLE and you win.

A man was found dead in his study. He was slumped over his desk and a gun was in his hand. There was a cassette recorder on his desk. When the police entered the room and pressed the play button on the tape recorder they heard: “I can’t go on. I have nothing to live for.” Then there was the sound of a gunshot. The police investigator said that the man is been murdered not a suicide.
The question is why they know that a man is been murdered not a suicide and why?
Note:
The first to answer it right will be the winner.

A man was found dead in his study. He was slumped over his desk and a gun was in his hand. There was a cassette recorder on his desk. When the police entered the room and pressed the play button on the tape recorder they heard: “I can’t go on. I have nothing to live for.” Then there was the sound of a gunshot. The police investigator said that the man is been murdered not a suicide.
The question is why they know that a man is been murdered not a suicide and why?
Note:
The first to answer it right will be the winner.
