Editor's Note: This article was updated in the afternoon of Apr 18 with information about the confirmation of ricin.

Apr 18, 2013 (CIDRAP News) – The FBI today confirmed the presence of the toxin ricin in letters intended for President Obama and other officials this week, following the agency's arrest of a Mississippi man yesterday in connection with the mailings.

"The FBI, through laboratory testing, has confirmed the presence of the toxin ricin in these letters. Further forensic examination is being conducted," the agency said in a statement this afternoon. The agency said no one was harmed by the letters.

In a statement yesterday, the FBI referred to suspect letters addressed to the White House, an unnamed US senator, and an unnamed Mississippi justice official. Media reports have listed Sen. Roger Wicker, R-Miss., as the intended recipient of a letter containing material that preliminarily tested positive for ricin.

In yesterday's statement, the FBI said Paul Kevin Curtis, 45, was arrested about 5:15 p.m. at his home in Corinth, Miss., about 100 miles east of Memphis. 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 agency said.

CNN reported today that Curtis was charged with sending a threat to the president. He was ordered to remain in custody until a preliminary and detention hearing on Apr 29, the story said.

A relative of Curtis said he was shocked by the arrest and described the suspect as a "super entertainer" who impersonated Elvis Presley and many other singers, according to a USA Today report today.

The story referred to numerous online statements by a man named Kevin Curtis who claimed to have uncovered a conspiracy to sell human body parts on the black market and alleged that unnamed government officials were trying to ruin his reputation.

In one post, Curtis said he had sent letters to Wicker and other politicians but had never received any replies, according to USA Today.

The letter to Wicker was reported Apr 16, and the letter to the White House was revealed yesterday.

Besides the letters to Obama and Wicker, suspicious packages were received yesterday at the Washington office of Sen. Richard Shelby, R-Ala.; the Saginaw field office of Sen. Carl Levin, D-Mich., and the Phoenix office of Sen. Jeff Flake, R-Ariz, according to media reports. Flake later said investigators had found there was no threat, according to USA Today.

See also:

Apr 18 FBI statement

Apr 18 CNN story

Apr 17 FBI press release

Apr 18 USA Today story