James Everett Dutschke, 41, of Tupelo entered a guilty plea under an agreement that calls for a 25-year federal prison sentence, CNN reported. He will be formally sentenced in about two months.
Ricin, a very toxic substance, occurs naturally in the seeds of the castor oil plant. It was used in 1978 in London to kill Georgi Markov, a Bulgarian dissident, with a ricin pellet delivered by means of an umbrella.
The letters to Obama and Wicker were discovered at a federal screening center. Lee County Judge Sadie Holland was the recipient of the third letter. No one was injured by the poisonous letters.
The letters, mailed from Memphis, Tenn., were signed "KC."
"To see a wrong and not expose it, is to become a silent partner to its continuance," the text said.
Notable deaths of 2014 [PHOTOS]
Hiker dead in apparent bear attack in New Jersey