Let it go. Whoever did it was acting on behalf of their government, not as a criminal, in an undeclared war. That war is over. So, under the Supreme Court’s new doctrine, the combatants in that war, unlawful though they may be, are entitled to be treated as POWs. Even if you found out who it was, you have to release them at the end of the war.
If you are ever hit by one of these, then get away as quickly and as safely as possible. Once in a safe location, remove the cyanide bee-bee (actually it is slightly larger than a conventional bee-bee) and there should be some (black) thread to remove along with it. If you do not remove it in 24 hours you will most likely be dead.
This is a very poor weapon against people of above average intelligence.
A little-known fact about this case is what Markov exactly said that so upset the Bulgarian authorities. It has been generally thought that Markov's anticommunist rants were to blame. Not true! The Bulgarians were plenty used to anticommunist criticism. No, what got Bulgarian authorities so hopping mad was the fact that Markov was broadcasting gossip about their personal lives -- e.g., extramarital affairs, bribes and graft, etc. He named names, and Bulgarians listened to the broadcasts with relish. So the killing was less political than commonly thought.