Some of those who attended are volunteers at the museum who said they didn't learnthe painting had been removed until they received theletters in the mail.
Law enforcement agents should be able to test the toxin found in theletters to determine its potency and purity, as well as learn what chemicals may have been used to extract it from widely available castor beans, said Murray Cohen, the founder of the Atlanta-based Frontline Foundation, which trains workers on preparedness and response to bioterrorism and epidemics.