Funny you should mention this b/c my mother was very disappointed in the ending as well. I am not exactly sure how they knew who the killer was, I think the actual putting together the pieces was left out for the reader. I enjoyed the book very much but I agree that the ending was a little anti-climatic. The other Patterson book that had a very disappointing ending for me was London Bridges.
The last one
I finally finished the book last night.
~Jackie, BookCrossing Member & Warming Families Volunteer