Factbox – Ricin: deadly, easily concealable poison

April 17 – Ricin, one of the deadliest poisons known, was found in a letter addressed to U.S. President Barack Obama, according to preliminary tests. Following are some key facts about ricin: – Ricin is made from castor beans, the same substance used to make castor oil. It can be found as a powder, mist, or pellet and is very difficult to trace. – Ricin is perhaps best known as the poison used to assassinate Bulgarian exile Georgi Markov in London in 1978. An agent injected Markov with a ricin pellet using a specially rigged umbrella. Markov died a few days later. – In the 1940s, the U.S. …