A Murder, not a Suicide

Crime scene:

In a house, a dead man with a gun in one of his hands and a recorder on the other.  A gunshot through his head.  No sign of violence. The detective in charge took the recorder and played it. 

"I'm tired of my life, I wanna die." *gunshot*

The detective asked the dead man's roommate, "Is this his voice?".  He replied, "yes".

The detective said "we must find the murderer".

How did the detective know it was a murder and not a suicide?

Think. 

<Post your answers on the comment box.  Thank you.>