Authorities said Wednesday they had intercepted a letter to the White House that tested positive for ricin poison.
The Secret Service acknowledged the letter addressed to President Obama contained a suspicious substance, and the FBI later said tests showed it was ricin, the same deadly toxin sent in a letter addressed to Sen. Roger WickerRoger WickerRyan praises FCC chief's plans to roll back net neutrality FCC head unveils plan to roll back net neutrality Rob Thomas: Anti-Trump celebs have become 'white noise' MORE (R-Miss.). The Wicker letter was made public on Tuesday.
"This facility routinely identifies letters or parcels that require secondary screening or scientific testing before delivery," the Secret Service said in a statement. "The Secret Service White House mail screening facility is a remote facility, not located near the White House complex, that all White House mail goes through."
The agency said it is working closely with the U.S. Capitol Police and the FBI in the investigation.
White House press secretary Jay Carney said Obama had been briefed twice on the investigation. "He was briefed last night and again this morning," Carney said.
News of the letter to Obama came at the same time Capitol Police were investigating three suspicious packages at Senate office buildings and two days after a terrorist bombing at the Boston Marathon left three people dead and more than 170 injured.
Police later said reports came back negative on the packages, which were reported on the third floor of the Hart and Russell Senate office buildings and the first floor of the Hart building. Senate sergeant at arms Terry Gainer told The Hill that the letters were reported as suspicious because they were hand-delivered and not screened by the mailing facility in Maryland beforehand.
In addition, Sen. Carl LevinCarl LevinFor the sake of American taxpayers, companies must pay their fair share What the Iran-Contra investigation can teach us about Russia probe Senate about to enter 'nuclear option' death spiral MORE's (D-Mich.) local Saginaw, Mich., office reported a suspicious-looking letter to law enforcement, a Levin aide told The Hill. In a statement, Levin said he did not know if the letter was a threat.
The letter was not opened, and law enforcement officials are now investigating it. The building was evacuated as a precaution, the aide said.
The FBI also said that a second and separate mail screening facility tested positive for ricin on Wednesday morning. The facility is being tested, according to the FBI.
“It is important to note that operations at the White House have not been affected as a result of the investigation," the FBI said. “The investigation into these letters remains ongoing, and more letters may still be received. There is no indication of a connection to the attack in Boston."
Fox News reported that like the letter to Wicker, the letter to Obama was sent from Memphis, Tenn. Fox News said the letters to Obama and Wicker contained similar language and are signed identically.
Security in Washington has been tightened since the Boston attacks, with visitors asked to take off their shoes before entering some Senate and House office buildings on Tuesday.
Of the letter sent to Wicker, Gainer said, “The letter was not outwardly suspicious, which is usually a clue.
“But we want Senate state office employees to beware of what we know, but they must be careful with all mail they open, follow the procedures with which they have been skilled,” he said.
Gainer said previously that the Senate's off-site mail facility has been closed as Capitol Police and the FBI investigated. Sen. Claire McCaskillClaire McCaskillFive takeaways from the Georgia special election Picking 2018 candidates pits McConnell vs. GOP groups Potential McCaskill challenger has .7M: report MORE (D-Mo.) said Capitol Police have a suspect who has been known to write letters to members of Congress.
On Tuesday, Senate Majority Leader Harry ReidHarry ReidDraft House bill ignites new Yucca Mountain fight Week ahead: House to revive Yucca Mountain fight Warren builds her brand with 2020 down the road MORE (D-Nev.) said he was aware only of the letter to Wicker.
“All we know now is just one,” Reid said, speaking to reporters after an intelligence briefing at the Capitol.
In 2004, a letter addressed to former Sen. Bill Frist (R-Tenn.) also tested positive for ricin after it was found to contain a white powder while being sorted in the Dirksen Senate Office Building. The Senate office buildings were closed and decontaminated, but authorities never solved the case.
Ricin is a poison found in castor beans that can be manufactured from the bean's waste materials, according to the Centers for Disease Control and Prevention.
“Ricin works by getting inside the cells of a person’s body and preventing the cells from making the proteins they need. Without the proteins, cells die. Eventually this is harmful to the whole body, and death may occur,” the CDC warns.
— Jordy Yager and Jeremy Herb contributed to this story.
— Published at 11:13 a.m. and updated at 1:00 p.m.