Think about it. Who profits? Other Serbs, muslims, the US, Russia?
The man had many enemies. I sound like a bad TV detective show, but that's the fact.
MEthinks he was about to finger somebody. Somebody big. Somebody couldn't afford to allow him to put on his defense. The Russians have been known to use these sorts of techniques, e.g., they Ricin Umbrella, and the Ukrainian dude that turned purple.