A Mississippi man has been arrested in connection with the mailing of three letters sent to President Obama, Sen. Roger Wicker, R-Miss., and a Mississippi official that tested positive for ricin.
After initial tests gave mixed results, a senior congressional source told Fox News on Thursday that the substance in the letters was "absolutely, unequivocally ricin." The source said the sample, in testing, came back "very hot."
The testing was apparently conclusive enough to charge the suspect. The Department of Justice said Paul Kevin Curtis, 45, was arrested at his Corinth, Miss., home Wednesday afternoon following an investigation conducted by an FBI Joint Terrorism Task Force and several other agencies.
The FBI confirmed earlier Wednesday that a letter addressed to Obama had "preliminarily tested positive" for ricin, a day after lawmakers said another letter sent to the Capitol Hill office of Wicker tested positive for the same substance.
Curtis believed he had uncovered a conspiracy to sell human body parts on the black market and sometimes performed as an Elvis Presley impersonator, the Associated Press reported.
The letters to Obama and Wicker said: "To see a wrong and not expose it, is to become a silent partner to its continuance." Both were signed, "I am KC and I approve this message."
Ricky Curtis, who said he was Kevin Curtis' cousin, said the family was shocked by the news of the arrest. He described his cousin as a "super entertainer" who impersonated Elvis and numerous other singers.
"We're all in shock. I don't think anybody had a clue that this kind of stuff was weighing on his mind," Ricky Curtis said in a telephone interview.
Ricky Curtis said his cousin had written about problems he had with a cleaning business and that he felt the government had not treated him well, but he said nobody in the family would have expected this. He said the writings were titled, "Missing Pieces."
Multiple online posts on various websites under the name Kevin Curtis refer to the conspiracy he claimed to uncover when working at a local hospital from 1998 to 2000.
The author wrote the conspiracy that began when he "discovered a refrigerator full of dismembered body parts & organs wrapped in plastic in the morgue of the largest non-metropolitan healthcare organization in the United States of America."
In one post, Curtis said he sent letters to Wicker and other politicians.
In a statement following the announcement of the arrest, Wicker thanked FBI and Capitol Police for their "professionalism and decisive action" in keeping his family and staff "safe from harm."
Wicker assured Mississippians that both his offices in Mississippi and Washington remained open for business and thanked the people of Mississippi for their thoughts and prayers.
The warnings about the letters came amid a flurry of reports on suspicious packages Wednesday, contributing to confusion and anxiety on Capitol Hill. Fox News learned of several suspicious packages or envelopes in various Capitol Hill office buildings, and Capitol Police said three packages that were flagged had been removed.
Separately, the office of Sen. Carl Levin, D-Mich., reported a "suspicious-looking letter" at one of the senator's Michigan offices, which later came back "negative"; and a spokesman for Sen. Jeff Flake, R-Ariz., reported a "suspicious letter" was intercepted at Flake's Phoenix office. Authorities were also called to the Dallas office of Sen. John Cornyn, R-Texas, over what was described only as "a piece of mail" -- but field tests later came back negative.
According to a Homeland Security Department handbook, ricin is deadliest when inhaled. It is not contagious, but there is no antidote. A senior Congressional source familiar with the inquiry into the letters sent to Obama and Wicker told Fox News that the ricin was "low grade" and "not weaponized."
The package alerts compounded security concerns in the wake of the letter incidents and the Boston bombing, which the FBI has said do not appear to be related.
Both of the initial suspicious letters were apparently intercepted on Tuesday. They never reached the Hill or the White House.
The envelopes had Tennessee postmarks, but no return address.
Obama's press secretary, Jay Carney, said mail sent to the White House is screened at a remote site for the safety of the recipients and the general public.
Senate Sergeant-at-Arms Terrance Gainer also said that an individual who was responsible for simultaneous suspicious-package incidents in the Hart and Russell Senate office buildings on Tuesday was detained and released on Wednesday. The packages were not hazardous.
Gainer said the man was "not particularly harmful, although terribly disruptive."
The mail-screening system was established after the Anthrax attacks of 2001 that closed the Hart Senate Office Building.
Fox News' Mike Emanuel and Chad Pergram, and the Associated Press contributed to this report.