Aamer Madhani, Peter Eisler and Kevin Johnson USA TODAY
WASHINGTON - The U.S. Secret Service is investigating a letter containing a "suspicious substance" that was addressed to President Obama, the agency confirmed on Wednesday, and at least three U.S. senators also reported receiving suspicious mail.
FBI spokesman Paul Bresson said preliminary tests on the letter to Obama showed evidence of ricin, a powerful toxin.
The letter was sent to Obama on Tuesday, and was intercepted at the White House mail screening facility, according to Secret Service spokesman Brian Leary.
The White House mail screening facility is a remote facility, not located near the White House complex, Leary said.
The revelation of the suspicious letter to Obama comes less than 24 hours after U.S. Capitol Police confirmed it was investigating a letter addressed to Sen. Roger Wicker, R-Miss., that tested positive for the poison ricin in a preliminary examination.
Obama was briefed on the suspicious letters on Tuesday night and again on Wednesday morning, said White House Press Secretary Jay Carney.
The FBI says there is no indication that the suspicious letters are connected to this week's double bombing in Boston. Carney cautioned that Americans shouldn't jump to any conclusions.
"Before we speculate or make connections that we don't know...we need to get the facts," Carney said.
Another suspicious package was received Wednesday morning at the Washington offices of Sen. Richard Shelby, R-Ala., according to Shelby's spokesman Jonathan Graffeo. He said the package is being investigated by Capitol Police and it was not known if it was similar to the ones addressed to Obama and Wicker.
Sen. Carl Levin, D-Mich., issued a statement saying that a suspicious letter also was received Wednesday morning at his Saginaw, Mich., field office. He said the staffer who received the letter did not open it and turned it over to authorities, who are investigating.
"We do not know yet if the mail presented a threat," Levin said.
The letter to Wicker, which was intercepted at an off-site Capitol mail facility, was found to contain a "white granular substance'' and was quarantined before a preliminary test indicated the substance was ricin, the statement said.
"The material is being forwarded to an accredited laboratory for further analysis," according to the statement authorized by U.S. Capitol Police Chief Kim Dine.
Bresson, the FBI spokesman, said that filters at one of the remote facilities used to screen official mail also tested positive for ricin this morning.
Anytime suspicious powder is located in a mail facility, field tests are conducted, Bresson said, but those tests can produce inconsistent results.
If the tests indicate the possibility of a biological agent, the material is sent to an accredited laboratory for further analysis, and only those tests can confirm the presence of a biological agent. Those tests are currently being conducted and generally take from 24 to 48 hours, Bresson said.
The U.S. Capitol Police alerted congressional staff just after noon that they were investigating a suspicious package in the atrium of the Hart Senate Office Building, as well as suspicious envelopes received in upstairs offices of both the Hart building and the nearby Senate Office Building. The message advised staff that they were not required to stay in their office, but to avoid the areas where the suspicious packages were being investigated.
An announcement in the buildings just before 1 p.m. said that test results on the packages were negative and closed off areas had reopened.
Scott Ongill, a Senate staffer, said such alerts are not unusual. "There is a couple, three (alerts) a week around the Capitol campus. It's not that uncommon an occurrence. They're doing due diligence." He said they usually end up being tourists who left something.
Kathy Windsor of Lebanon, Mo. , was in Washington, D.C., to lobby on a bill with Missouri lawmakers including Sen. Claire McCaskill. "They will not let us in the building," she said. She was told Hart was closed "until further notice." "With what's happened this week they have to take everything seriously," Windsor said.
Contributing: Mary Orndorff Troyan, Deirdre Shesgreen, Deborah Barfield Berry and Maureen Groppe of the Gannett Washington Bureau.