Updated Wed, Apr 17, 2013 12:42 pm
UPDATE 12:30 p.m. The FBI says the letters sent to President Barack Obama and Sen. Roger Wicker are related and are both postmarked out of Memphis, Tenn., dated April 8.
In an intelligence bulletin obtained by The Associated Press, the FBI says the letters both say: "To see a wrong and not expose it, is to become a silent partner to its continuance." Both letters are signed, "I am KC and I approve this message."
The FBI says the substance in both letters have preliminarily tested positive for ricin, a potentially fatal poison.
Both the letters to Wicker, R-Miss., and to Obama were intercepted at off-site mail facilities.
The FBI says it is pursuing investigative leads to determine who sent the letters.
The FBI says preliminary tests on a letter sent to President Barack Obama indicate the presence of poisonous ricin.
The letter is undergoing further testing because preliminary field tests can be unreliable, creating false positives.
The letter was intercepted at a facility away from the White House. It comes the day after officials said a letter sent to Sen. Roger Wicker tested positive for poisonous ricin. That letter to Wicker, a Republican, was intercepted at a Senate mail facility just outside Washington.
The FBI says there is no indication of a connection to the bombing at Monday's Boston Marathon.