A letter addressed to President Barack Obama containing a suspicious substance was intercepted and is being tested, according to the Secret Service.
Tuesday, the FBI said that a envelope testing positive for ricin, a deadly poison, was intercepted at the U.S. Capitol and addressed to Sen. Roger Wicker (R-MS).
In the first case, the letter was intercepted at a postal facility in Maryland that screens mail sent to Congress, and never reached Wicker’s office.
Sen. Wicker thanked law enforcement and said an investigation was underway. The White House's mail is screened at a separate, offsite facility.
Other U.S. Senators were made aware of the Wicker letter during a briefing on the Boston Marathon bombing, which is not believed to be related.
Sen. Claire McCaskill (D-MI) said that the person who sent Wicker the letter writes often to elected officials, though no one is believed to be in custody.
The Wicker letter was postmarked Memphis, Tenn., with no return address.
Ricin poisoning can kill within 36 hours, and there is no known antidote for it. It is unclear if the letter sent to Obama also contained ricin poisoning.