A few years back, I was writing a somewhat bad novel when I had occasion to kill off my prime suspect. It had to be by a poison that was not fast-acting and would leave no trace. The infamous umbrella murder came to mind. In 1978 Georgi Markov, Bulgarian exile, was killed by a pellet of ricin embedded in his leg by the tip of an umbrella. The poison was identified, not by what was in his system at the time of death, but by the residue in the actual pellet itself. Here then was a poison that could be administered either through inhalation or ingestion. There is no cure, as far as I know. It is a matter of dosage.
So it was scary when police in London, site of the Markov assassination, found ricin in the apartment of a purportedly Al Queda-affiliated group. On this side of the Atlantic, we have our own ricin stories. A woman murdered her husband feeding him ground up Castor beans or some such. And more recently, ricin was found in a Las Vegas hotel room, after a guest sickened. Roger Bergendorff, that guest, was arrested today after being released from the hospital. It seems he manufactured the ricin from Castor beans in his cousin's basement, presumably in his underwear. Castor beans are legal; ricin is not. Still missing- the "why"? Stay tuned, this should be an interesting story.
AP story about the last case here.