Castor beans (shown on top) are used to produce ricin, a deadly poison, as pictured in this handout photo from the National Counter Terrorism Centre. They are similar in color and size to pinto beans (shown on bottom), but have a small pointed protrusion on the end. Photograph: National Counter Terrorism Centre/Handout/Reuters

Federal prosecutors have filed criminal charges against Paul Kevin Curtis, the Mississippi man who was arrested a day earlier in the FBI's inve(...)

 An official walks past a hazardous materials response team truck outside a mail sorting facility in Hyattsville, Maryland. An envelope addressed to US Senator Roger Wicker  tested positive for ricin at the facility where mail bound for the US Capitol is sorted. Photograph: Drew Angerer/Getty Images

The FBI arrested a Mississippi man yesterday in connection with letters sent to President Barack Obama and two other officials that are believe(...)