His sponsors need an excuse for intervention on his behalf. Let's start with a motive for the assassination. There isn't one. Which is why they fail. They were meant to fail.
Dead martyrs are useless as vassals.
The entire assassination scenario, as outlined to the western media last night by Draskovic himself, reads like a bad plot for a third-rate fiction novel. But let's accept Draskovic's claim at its face value. You believe the regime in Belgrade is about to kill you. You leave Serbia and go to a supposedly safer Montenegro where your pal Djukanovic is in charge. You even leave your wife in Serbia, presumably for her own safety.