Holy crap did anyone else catch this? At the very beginning when you first use detective mode to follow Frank Boles’ evidence trial you come upon a reception room (hint: its right before the room with the elevator and Harley Quinn cut scene). Well in that room you hear the phone ringing and it is a woman calling asking if anyone has seen her husband (or boyfriend, I don’t remember) because she heard something was going on. The Joker answers and say something like “I will pass on the message when I see him, but I can only find his head, I’ll get back to you when I find the rest of him”.
Well, later on in the game when you get to the medical facility, you’ll reach the Sanatorium where you have to use your predator skills to save the two doctors. After you save the two doctors explore the rooms. In one of the offices (the room where you find patient interview #21 for the riddler), you’ll come across a jar with a severed head in it. This has to be the head the joker was talking about to that poor woman looking for her husband!!!