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.
Ain't the Russians this time.
The Ricin Umbrella attack was a Bulgarian operation - which was also the outfit that many blame for the attempt on the Pope's life. It could have been the KGB that showed them how or they came up with the technique on their own.