Demarkov is former KGB
I don't see this in any of the discussions, but when Jack is trying to find Demarkov he goes through old police files. A lot of what he finds is printed in Russian. One of the documents has a shield printed on the letter-head. The shield is black, red and yellow on white and displays a sword with a single star at the hilt. If I'm not mistaken this is the symbol for the KGB.
When I saw that I knew Demarkov was going to be deadly and unpredictable.
Warning: I probably read the book first.