When the killer rings Ironside while he's waiting in the police van, he asks if Ironside recognises his voice. Ironside replies, "Yes, I do recognise your voice!" while reaching up and starting the tape recorder. The tape starts as the killer says, "I wanted to wait till you were alone." However when the tape is played back at the police station, it has recorded Ironside confirming that he recognises the killer's voice - which was said before the tape was running.