A Mississippi man accused of mailing letters with suspected ricin to national leaders believed he had uncovered a conspiracy to sell human body parts on the black market and sometimes performed as an Elvis Presley impersonator.

Paul Kevin Curtis, 45, was arrested Wednesday at his home in Corinth, near the Tennessee state line about 50 miles north of Presley's birthplace in Tupelo.

Authorities were waiting for definitive tests on intercepted letters that were addressed to President Barack Obama and Sen. Roger Wicker, R-Miss. Preliminary field tests can often show false positives for ricin. Ricin is derived from the castor plant that makes castor oil. There is no antidote and it's deadliest when inhaled.

An FBI intelligence bulletin obtained by The Associated Press said the two letters were postmarked Memphis, Tenn.

Both letters 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."

The letters had Washington on edge in the days after the Boston Marathon bombing. As authorities scurried to investigate three questionable packages discovered in Senate office buildings Wednesday, reports of suspicious items also came in from at least three senators' offices in their home states. The items were found to be harmless.

In Corinth, a city of about 14,000, police cordoned off part of a subdivision where Curtis lived. At least five police cars were on the scene, but there didn't appear to be any hazardous-material crews and no neighbors were evacuated. The one-story, single-family home is similar to the others in the neighborhood, with red brick with white trim.

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."

A MySpace page for a cleaning company called The Cleaning Crew confirms that they "do windows" and has profile photo of "Kevin Curtis, Master of Impressions." A YouTube channel under the name of Kevin Curtis has dozens of videos of him performing as different famous musicians, including Elvis Presley, Buddy Holly and Kid Rock.

"As far as him being anti-government, I'm not going to say that, but he had some issues with some stuff that happened with his cleaning business," the cousin said.

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."

Curtis wrote that he was trying to "expose various parties within the government, FBI, police departments" for what he believed was "a conspiracy to ruin my reputation in the community as well as an ongoing effort to break down the foundation I worked more than 20 years to build in the country music scene."

In one post, Curtis said he sent letters to Wicker and other politicians.

"I never heard a word from anyone. I even ran into Roger Wicker several different times while performing at special banquets and fundraisers in northeast, Mississippi but he seemed very nervous while speaking with me and would make a fast exit to the door when I engaged in conversation..."

He signed off: "This is Kevin Curtis & I approve this message."

The FBI said there was no indication of a connection between the letters and the Monday bombing in Boston that killed three people and injured more than 170. The letters to Obama and Wicker were postmarked April 8, before the marathon.

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. He declined to comment on the significance of the preliminary ricin result, referring questions to the FBI.

At a House hearing, Postmaster General Patrick Donahoe noted there had been ricin alerts since the notorious 2001 anthrax mailings and procedures are in place to protect postal employees and help track down culprits.

"Over the course of years we've had some situations where there have been ricin scares," Donahoe said. "Until this date, there's never been any actually proved that have gone through the system."

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Associated Press writers contributing to this report from Washington were: Eileen Sullivan, Laurie Kellman, Donna Cassata, Henry Jackson and Eric Tucker.