 FACT: It is stated that the record on the turntable was still  playing when the body was discovered. This would not have happened  because the turntable is a record changer that automatically shuts  off when the control arm is engaged and there are no more records in  the stack. In the flashback sequence, Harry Prebble is shown  activating the control arm. If it had been left disengaged (up and  to the side) it would have played the record continuously as  mentioned.