Barack Obama
Both letters read, "To see a wrong and not expose it, is to become a silent partner to its continuance" and were signed "I am KC and I approve this message." A few granules of ricin can kill a human being in a matter of days. The matter is being investigated by the Secret Service.
It is worth noting, around the time of the September 11th terrorist attacks, letters containing ricin were mailed to members of Congress as well. The ricin laced letters sent this month on April 8, 2013, arrived close to the time of the Boston Marathon bombings, revealing a similar pattern of criminal conduct. Thus far, the government has announced no suspects in the case and no terrorist organization has claimed credit for the heinous attack on Boston.