The FBI on Wednesday said initial analysis indicates that a suspicious substance mailed to President Obama was the toxin ricin, Reuters reported.
The envelope "containing a granular substance that preliminarily tested positive for ricin," according to an FBI statement. The letter did not reach the White House.
The screening site where the envelope was found "routinely identifies letters or parcels that require secondary screening or scientific testing before delivery," Secret Service spokesman Edwin Donovan said. "The Secret Service is working closely with the U.S. Capitol Police and the FBI in this investigation."
Suspicious parcels were also reported on Wednesday at the Hart Senate Office Building.and the office of Senator Richard Shelby (R-Ala.), the Washington Post reported. None of those ultimately proved dangerous, according to Reuters.
There were also reports of questionable packages sent to home-state offices of Senator Carl Levin (D-Mich.) and Arizona Republicans John McCain and Jeff Flake, the National Journal reported. The envelope that arrived at Flake's office in Phoenix did not contain a dangerous substance, ABC News reported.
The reports come one day after early field testing indicated the presence of the lethal poison ricin in a letter sent to the office of Senator Roger Wicker (R-Miss.). The Obama and Wicker letters were said to appear alike, the Associated Press reported.
Senator Claire McCaskill (D-Mo.) said in a Tuesday AP report that investigators have identified an individual they believe is responsible for the first incident, though she did not disclose if the suspect had been apprehended. The suspect often sends letters to legislators, according to McCaskill.
Ricin is a byproduct of castor beans, is lethal in tiny amounts and has no known antidote. The relative ease of producing ricin from commonly found materials makes it a possible biological weapon. However, previous efforts by government biowarfare initiatives have had difficulty weaponizing the toxin for use in a large-scale attack.
The Senate's mail office in Maryland informed Capitol Police that "it had received an envelope containing a white granular substance," the law enforcement agency's spokesman, Shennell Antrobus said on Tuesday. "The envelope was immediately quarantined by the facility's personnel and [Capitol Police] HAZMAT responded to the scene."
Further testing of the material is needed as the initial field analysis came back with differing findings. That analysis is taking place at an accredited scientific facility, according to FBI spokesman Paul Bresson. Once this testing is complete, it should be definitively known whether the material is ricin, he said.
The envelope containing the substance was mailed from Memphis, Tenn., but there was no sender's address, according to Senate Sergeant-at-Arms Terrance Gainer. There are no signs of other possible ricin mailings, he said.
McCaskill credited the letter screening process put in place after the anthrax mailing attacks for stopping another biological incident, Reuters reported. In fall 2001, envelopes containing anthrax spores were mailed to lawmaker offices and news organizations, killing five people and sickening 17 others.
"The bottom line is the process we have in place worked," said the Missouri lawmaker.
None of this week's incidents are believed linked to the Monday bombing at the Boston Marathon, the National Journal reported.