WASHINGTON - 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."
What is ricin? A
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 there is no indication of a connection to the bombing at Monday's Boston Marathon.
Police investigate suspicious letters in Arizona
Authorities are investigating two suspicious letters that were sent to the Phoenix office of U.S. Sen. Jeff Flake of Arizona.
Emergency crews in hazardous materials gear rushed to the scene and evacuated people in parts of the building, located in the trendy Biltmore neighborhood of Phoenix.
Police spokesman Tommy Thompson says there were two suspicious packages and authorities are trying to find out if they are dangerous.
The situation came a day after authorities said a letter containing ricin was mailed to the office of a Mississippi senator. The Secret Service also says it has intercepted a letter addressed to President Barack Obama that contained a suspicious substance.
Flake is a Republican who was elected to the Senate last year.