WASHINGTON (USA TODAY) -- A letter addressed to Sen. Roger Wicker, R-Miss, tested positive for ricin poison, says Senate Majority Leader Harry Reid, D-Nev.
In a press release, Sen. Reid has said, "This matter is part of an ongoing investigation by the United States Capitol Police and FBI. I want to thank our law enforcement officials for their hard work and diligence in keeping those of us who work in the Capitol complex safe. Gayle and I appreciate everyone's thoughts and prayers."
The envelope, which was intercepted at an off-site Capitol mail facility, tested positive three times, according to the Associated Press.
The United States Postal Service has said it is still working with authorities on this matter and there are "no other reports of other such letters in the mail."
Senators were briefed on the threat in a closed-door meeting Tuesday night. Coming a day after two blasts killed three and wounded 176 people at the Boston Marathon, the ricin-tainted letter spurred renewed fears about terrorism.
Senator Claire McCaskill said authorities have a suspect, but she did not say if an arrest had been made. Terrance Gainer, the Senate sergeant-at-arms, said in an emailed message to Senate offices that the envelope had no obvious suspicious outside markings, bore a Memphis, TN., postmark and had no return address.
While reluctant to talk about the investigation, senators said it was reminiscent of the 2001 anthrax scare that followed the terrorist attacks on the World Trade Building and the Pentagon.
Ricin, a poison from the same bean used in castor oil, must be ingested to be fatal, says Milt Leitenberg, a University of Maryland bioterrorism expert.
"We were told it's not as deadly as Anthrax, but it's still very serious," said Senate Majority Whip Dick Durbin, D-Ill. The letter was intercepted at a suburban Prince Georges County, MD., mail facility.
"Everything that's sent to us, everything that's mailed to us, is roasted, toasted, sliced and opened," Durbin said.
Sen. Tom Coburn, R-Okla., ranking Republican on the Senate Homeland Security Committee, said there did not appear to be an ongoing threat.
In a 2010 report to Congress after the substance was singled out by the Department of Homeland Security for its possible application as a weapon of terror, the Congressional Research Service said exposure to ricin elicits various symptoms, depending on the type of exposure.
"Ingestion of ricin causes nausea, vomiting, diarrhea, gastric hemorrhaging, and shock,'' the report stated. "Injection of ricin produces severe internal bleeding and tissue death, which can result in the collapse of major organ systems. Death often follows such a collapse.''
Inhalation of the substance "irritates lung linings and airways, leading to weakness and fever.''
Gregory Korte and Kevin Johnson, USA Today. Contributing: Gary Strauss; Associated Press