Federal officials believe the same person has sent letters possibly contaminated with poisonous ricin to President Obama and a Republican senator from Mississippi, bearing the signature "I am KC and I approve this message."
Both mailings were intercepted at off-site locations and did not make it to the White House or Capitol. The substance inside both was shown to be ricin in preliminary tests, but further testing is needed to confirm.
"A letter addressed to the president was received at a remote screening facility containing a suspicious substance. We are working closely with Capitol Police and the FBI in this investigation," a Secret Service spokesman said.
Officials say the letter to Obama and the mailing to Sen. Roger Wicker were both postmarked Memphis, Tenn. and were mailed on April 8 before being intercepted Tuesday. Each has identical wording, including the phrase "to see a wrong and not expose it, is to become a silent partner to its continuance."
The FBI said there was "no indication of a connection" to the Boston Marathon bombings.
White House spokesman Jay Carney said the president has been briefed on the mailings.
The FBI warned that more letters could have been sent.
Ricin is a poison found in castor beans.
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