Sherlock breaks into a crime scene

Sherlock 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, Sherlock hears the message
'I have committed sins in my life and now I offer my soul to the
great lord'....following a gunshot.
Sherlock smiles Of-course its a murder.

Why did he think so?

Click here for Answer

There would be someone who rewinded the tape after the murder.