Crime scene

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In a condo unit, a dead man with a gun on 1 of his hands and a recorder on the other. A gun shot thru his head. Np sign of violence. The detective in charge took the recordder and played it. "Im tired of my life, i wanna die..." *gunshot* The detective ask the deadman's inmate "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 suicide?