Okay I think the psychiatrist Robben is Kister's brother and is the one who is actually responsible for all the murders and he is the so called "copycat murderer" and the "I'M BACK" is actually him starting the murders again and so the last victim was gonna be Jonathan and when Kister saw the "I'M BACK" he wanted to come back to actually save Jonathan but pretended that he was annoyed someone was copying him and I also guess the call Kister recieved was from Robben and maybe Baron actually found out about Robben and so Robben was trying to frame Baron and so to not get caught and to expose Robben, Baron escaped. Idk how much is actually true but just a theory.
Okay I think the psychiatrist Robben is Kister's brother and is the one who is actually responsible for all the murders and he is the so called "copycat murderer" and the "I'M BACK" is actually him starting the murders again and so the last victim was gonna be Jonathan and when Kister saw the "I'M BACK" he wanted to come back to actually save Jonathan but pretended that he was annoyed someone was copying him and I also guess the call Kister recieved was from Robben and maybe Baron actually found out about Robben and so Robben was trying to frame Baron and so to not get caught and to expose Robben, Baron escaped. Idk how much is actually true but just a theory.