If I were Putin, and all I wanted was for somebody to be knocked off, I'd drop a few hundred bucks on some thug to shoot the guy from an alleyway.

You're right in that this method does seem to narrow the list of suspects considerably. It's the equivalent in fiction of finding somebody who had been killed by sharks with laser beams on their heads, or shot in the old West with a silver bullet. Gee, I wonder who did that?

We are either looking at an elaborate framing setup, which is a bit weak considering the Russian record in this area already, or a situation where Russia damn well wants everyone to know who killed this guy and why, and that nobody can do anything about it. That's going to put some fear into a lot of people who could make trouble for Russia.

Which, come to think of it, is exactly why Dr. Evil or the Lone Ranger would leave a calling card.