The FBI, Capitol Police and the U.S. Postal Inspection Service are investigating dozens of letters containing suspicious materials sent to "several different addresses, including congressional offices." This is according to a notice received by senior staff at Senate offices and reported by NBC. "Law enforcement agencies are working to intercept any additional letters before they arrive, however some of the letters may reach their destination," the notice stated. According to the report, one of the senators whose office received a suspicious letter was Democratic Minority Leader Chuck Schumer. Three law enforcement sources briefed on the matter told NBC that initial tests of the material showed it is not dangerous.