What killed Georgi Markov?

Taken from http://search.gallery.yahoo.com/search/corbis?p=skull+and+crossbones&r=all

The pellet indicated the use of poison, but which one?  The pellet could only hold 0.4 grams of material. This ruled out inorganic poisons, since the deadliest of these, such as cyanide and arsenic, required a minimum of 100 milligrams to kill a human.  Around 50 milligrams of the deadliest organic poisons, such as fluoroacetates, would be needed.  Even with nerve gases, such as sarin, at least 1 milligram would be needed.

Germ warfare agents were also discounted because of the absence of lesions attributable to such agents.

This, therefore, left the choice between biological toxins, lethal agents extracted from plants and animals, and radioactive emitters.  The pellet provided another clue ? it had two holes.  One hole would have been sufficient to carry a lethal dose of a deadly radioactive agent, such as plutonium 239, and it would be relatively easy to detect.  If a biological toxin was used, it would require a hole for a supporting medium as well as a hole for the toxin.  Markov?s symptoms before he died ? high fever and vomiting ? were also consistent with the effects of a biological toxin.

All of the evidence pointed towards ricin, a derivative of the castor bean.  In order to test this theory, scientists injected a pig with the same dose of ricin Markov would have received.  The unfortunate beast died twenty four hours later, exhibiting the same symptoms as Markov.

No ricin was found in Markov?s body.  However, this provided more evidence for its use, since the body?s natural protein making cells break ricin down, leaving no trace of it in the body.

Having discovered the poison used, the police set out to catch the killer.