Death to a Tenor

Ronnie Ray became world famous as The Singer in the Dark, but even advertising agent Pete Hunter thought that was nothing but a publicity stunt until he found Ronnie's corpse seated in a homemade electric chair in a lonely roadside inn, three weeks after the tenor's strange disappearance. Though he was dead, how could his fiancée hear Ronnie sing a song that was not published until after his death in the voice that no one could imitate?