Mississippi (REUTERS) - A Mississippi man accused of sending poisoned letters to President Barack Obama and two other public officials, and then pinning them on an Elvis impersonator, pleaded guilty in US court and agreed to a 25-year jail sentence, the Justice Department announced on Friday.

James Everett Dutschke, 41, has been jailed since his arrest last April, when authorities accused him of sending ricin-tainted letters to President Obama, US Senator Roger Wicker of Mississippi and a local Lee County judge, Sadie Holland.

Ricin is a highly toxic protein found in castor oil plants that can kill an adult human in tiny doses.

Dutschke, a former martial arts instructor and one-time political candidate, originally had denied the charges but on Friday changed his plea in US District Court in Oxford, Mississippi, according to a Justice Department press release.

"It's closure, and any time you can get that it's a good thing," said Lee County Sheriff Jim Johnson, whose department had assisted the FBI and other agencies in identifying and arresting Dutschke last April.

The guilty plea "has eased our community and eased our victims and the other people he could have come in contact with," said Mr Johnson, who described Dutschke as a manipulator who thinks he can "outsmart any person of authority or any system".

Dutschke's attorney, Mr Ken Coghlan, said the plea agreement involved resolution of outstanding state charges of child molestation.

"He (Dutschke) was facing a lot of uncertainty and at least now he knows where he stands," said Mr Coghlan, noting that his client faced a maximum penalty of life in prison.

Under the agreement, Mr Coghlan said Dutschke would plead guilty to the molestation charges next week and would serve his sentences concurrently in federal prison.

Dutschke pleaded guilty to four charges of developing and possessing the biological agent ricin and subsequently mailing ricin-laced, threatening letters, including one that threatened bodily harm to the president of the United States.

Only Ms Holland received one of the letters. The US Postal Service intercepted those that were sent to Mr Obama and Mr Wicker.

The plea agreement was announced by Mr John Carlin, acting assistant attorney general for national security; Ms Felicia Adams, the US attorney for the Northern District of Mississippi; and Mr Daniel McMullen, special agent in charge of the FBI's Jackson field office.

Dutschke will be sentenced in about 60 days, the Justice Department said.

Dutschke previously had pleaded not guilty to five counts of a grand jury indictment and denied sending the letters.

He also pleaded not guilty on Dec 3 to a new charge that he tried to continue the scheme from jail.

An initial indictment in June said Dutschke tried to frame Mr Paul Kevin Curtis, an Elvis impersonator, by lifting phrases from Mr Curtis's Facebook account to make it look as though he was responsible for the letters.