The recorder- Detective Riddle

Detective Mehul breaks into a crime scene. The victim is the owner who is slumped dead on a chair and have a bullet hole in his head. A gun lies on the floor and a cassette recorder is found on the table. On pressing the play button, Mehul hears the message 'I have committed sins in my life and now I offer my soul to the great Lord and followed a gunshot Mehul smiles and informed the police that it's a murder.

Why did he think so?

How can a dead person rewind back the tape himself? How can a dead person rewind back the tape himself?