Feds Probe Ricin Mailings Federal authorities investigate three incidents in which the poison ricin apparently was sent through the mail. Last fall, ricin was found at a South Carolina postal facility, and an attempt was made to send the deadly toxin to the White House. On Monday, ricin was found in the offices of Senate Majority Leader Bill Frist. Experts say analysis of that sample could provide clues about who sent it. Hear NPR's Joe Palca.