In terms of structure, the third part half fulfils a promise made to the listener. That promise being that the case will be solved by the end. Structure, in this case, refers to Orson Scott Card’s M.I.C.E. quotient. For more information, you can read How to Write Science Fiction and Fantasy from a local library or check out a Writing Excuses podcast on the subject.
This story being primarily a mystery means that it’s an Idea story. Of course, the first scenes we get are about the characters. The “C” in “M.I.C.E.” Mary Robinette Kowal talks about how this quotient is like web code. The code for The New York Crimes might look something like:
<c><i>NYCrimes</i></c>
Where c is Character and “i” is for Idea.
A crude example, but it gets the message across. Anyway, the fulfilment of the “idea” aspect seemed tacked on, but it did feel like the writer almost forgot about it. It would be like never finding out who the murderer is in a classic whodunit story. This is a problem that The Dark Knight Rises has with its villain.
The cliffhanger ending works as we wrapped up the “idea” plot and now, based on the final scene at the bar, the next part the story will wrap up the “character” one.