Letters laced with the poison ricin, like the letters sent to a US Senator, were also sent to President Obama. At its most dangerous, ricin can kill a victim 6 to 12 hours after exposure, and there is no antidote. However it is extremely difficult to deliver a killer dose.
CNN reported that the letters read "To see a wrong and not expose it is to become a silent partner to its continuance." Signed: "I am KC and I approve this message." Read more at www.abcnews.go.com