I have a question

I always assumed it was that moment when Zuckerman came face to face with Coleman's and Faunia's killer. After leaving him out on the ice, Zuckerman obviously called the police as the scene where Faunia's ex is talking to the woman about killing them was done either in prison or at an insane asylum after the story was presumably over with.

I've just seen the film immediately after reading the book. The point of this final scene is that, although the ex-husband didn't get charged with any crime, the writer wants him to know that he knows what he did. In the book there's much more of a sense of threat to this scene - the writer knows that the ex-husband has picked up on the fact that he knows that he killed Silk and Faunia and gets really scared that the ex-husband might kill him before he even gets back to his car and shove his body down one of the holes in the ice.