Murder Riddles

The suicide cassette

Wailing police sirens and the blue and red lights were outside 26 Jupiter Avenue, where a supposed suicide had taken place.
The body of a well known journalist was found with a gun wound to the head in his study, a 38 caliber in his hand, with a cassette recorder in front of him.
The police were puzzled, why the Detective Inspector Wallace was taking such an interest in a silly city suicide. I mean, it was quite evident that the man had taken his own life, but he clearly stated that there was more to his death.
DI Wallace pressed play on the cassette recorder.
"I suppose you have found my body, if you are hearing this," sobbed the cassette recorder,"but, I have nothing left to live for. Goodbye" stuttered the journalist voice crackling from the black object, his voice chocking and sobbing.
A gunshot echoed through the room, making the Police jump, but it had been emitted by the Cassette recorder.
Silence followed, the room full of suspense, only to be broken by one of the new members of Scotland Yard.
"There you have it, a suicide. He said it himself! 'I have nothing left to live for'" quoted he, then making his fingers form the shape of a gun, putting it to the side of his head, mimicking the sound of a gunshot.
"Ah, that is were you are mistaken. It is quite clearly, a murder." Said Inspector Wallace.

What made him think this?
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