The main character Leo went through several obstacles and setbacks in his life & investigation of these murders but also received some revelations that let the reader believe he will lead a better life. The turn at the end was it was actually Leo's brother that was committing the murders as a way to bring his brother back to him. The brothers were separated during a time when everyone was starving, Leo was kidnapped for food but ended up replacing the child the other family was trying to save. Leo was raised by this new family and became a star of the USSR in WWII and afterwards in the Secret Police.
Andrei, the brother left behind, was clumsy and could hardly see. His mother blamed him for his brother leaving them, Pavel(Leo's real name) was his mothers favorite. Eventually Andrei somehow survived the winter and received glasses so he wasn't the clumsy kid of youth. He obviously had several issues and turned to killing kids and butchering them as a way to lure his brother in. Not sure that I really believe this, but since Andrei was in a very real sense insane, I guess I can see how he might have believed this.
Like I said a good book and very interesting stuff going along with the main story line as well. It is a WL book on PBS so I should be mailing it off in the next few days as well.