FBI arrests Mississippi man in ricin letter plot

The FBI arrested a Mississippi man on Wednesday that it "believed to be responsible" for mailing letters containing the poison ricin to President Obama, Sen. Rocker Wicker (R-Miss.) and another official.

The FBI said that Paul Kevin Curtis was arrested at his home in Corinth, Miss., on Wednesday.

Curtis is "the individual believed to be responsible for the mailings of the three letters sent through the U.S. Postal Service which contained a granular substance that preliminarily tested positive for ricin," the FBI said.

A letter containing ricin was sent to Wicker on Tuesday but was intercepted at the Senate Mail Handling Facility before it reached Capitol Hill.

A second letter, found on Wednesday, also contained a substance that preliminary tests found to be ricin. The letter, which was addressed to Obama, was found at an offsite mail screening facility and was immediately quarantined by U.S. Secret Service personnel.

Several other senators also reported receiving suspicious mail, prompting U.S. Capitol Police to briefly close parts of two congressional office buildings.

Bother letters included the same message - "To see a wrong and not expose it, is to become a silent partner to its continuance," and are signed "I am KC and I approve this message," the Associated Press reports.

Senate Sergeant-at-Arms Terrance Gainer said that there is currently no indication that the letters were tied to the Boston Marathon bombing.

Capitol Hill police are investigating a suspicious package received by the Washington offices of Sen. Richard Shelby (R-Ala.). Sen. Jeff Flake (R-Ariz.) also reported receiving suspicious letters, while Sen. Carl Levin (D-Mich.) issued a statement that his Saginaw, Mich. office received a suspicious letter on Wednesday morning.

"Earlier today, a staffer at my Saginaw regional office received a suspicious-looking letter," Levin said. "The letter was not opened, and the staffer followed the proper protocols for the situation, including alerting the authorities, who are now investigating. We do not know yet if the mail presented a threat. I'm grateful for my staff's quick response and for government personnel at all levels who are responding."