A day after U.S. Capitol mail screeners found a ricin-laced letter addressed to Sen. Roger Wicker (R-Miss.), the U.S. Secret Service found a parcel addressed to President Obama that contained a “suspicious substance.” The Associated Press reports that the letter addressed to Obama is very similar to the one sent to Wicker.

The letter to Obama was intercepted yesterday at an off-site mail facility. Mail to both the White House and the Capitol are screened at separate locations. News of the substance-laden letters comes just two days after a pair of bombs were detonated at the finish line of the Boston Marathon, killing three and injuring more than 170. There is no indication of any connection between the letters and the explosions in Boston, the FBI says in a news release.

Meanwhile, U.S. Capitol Police also found a suspicious letter addressed to Wicker’s fellow Mississippian, Sen. Richard Shelby. Capitol Police have a suspect for the letters though, Sen. Claire McCaskill (D-Mo.) told reporters last night. McCaskill, the AP reports, said the parcel marked for Wicker came from a person “who writes a lot of letters” to members of Congress.

Additionally, parts of the Hart Senate Office Building have been locked down following the discovery of a suspicious package in the lobby.