Desmostylus, the toxicity of ricin is pretty well established … among other things, it was the poison used in the infamous “poison-tipped umbrella” assassination of Georgi Markov. The pinhead-sized capsule injected into Markov’s leg apparently contained 450-500 micrograms of the stuff; the lethal dose is around 1 microgram per kilo of body weight.
It’s a lethal toxin, relatively simple to prepare, and extracted from a common plant … bluntly, the Iraqis did have, and terrorist networks do have, the ability to produce it. Of course, so does the chemistry lab in the average high school.