Speaking at a press conference a little after noon, White House Press Secretary Jay Carney said that as the FBI and Secret Service had indicated, a letter addressed to the President, which was at an offsite mail facility, was found to contain a suspicious substance and further tests were being conducted. That follows reports of a similar letters to Senator Wicker that was stopped at mail facilities and reported by the Capitol Police, he noted.
UPDATE: U.S. Capitol police were questioning an individual who delivered at least two suspicious packages to Senate office buildings, Sergeant at Arms Terence Gaine said," reported New York Daily News earlier today. About 1pm, reports the New Hampshire Union Leader, U.S. Capitol Police "announced the Hart Senate Office Building has reopened after the substance found there tested negative."
With regard to the investigation into the Boston bombing, Carney noted that the investigation was not even 48 hours old. He encouraged everyone to let the investigation into the Boston bombings run its course. There will be an FBI briefing on the ground in Boston later today, he noted. The FBI is heading both investigations.