US prosecutors dropped charges on Tuesday against a Mississippi man accused of sending ricin-laced letters to President Barack Obama, a US senator and a state judge, according to court documents.

The surprise decision came hours after Paul Kevin Curtis was released from a Mississippi jail on bond.

Prosecutors said the "ongoing investigation has revealed new information," but provided no additional details, according to the court order dismissing the charges.

Curtis told reporters he respected Obama. "I would never do anything to pose a threat to him or any other US official," he said. "I love this country."

He said he had no idea what ricin was. "I thought they said 'rice,' I told them I don't eat rice," he said.

Curtis, who is 45 and known in Mississippi as an Elvis impersonator, had been released from jail on bond earlier on Tuesday after a judge indefinitely postponed a court hearing on his detention. The case was later dismissed "without prejudice," meaning the charges could be potentially reinstated if warranted.

Later on Tuesday federal law enforcement officials searched the house of a second Mississippi man, Everett Dutschke, Lee County Sheriff Jim Johnson told Reuters.

It was not clear if the search was related to the ricin case.

A representative for the US Attorney's Office in Oxford, Mississippi, did not return calls for comment.

Dutschke is "cooperating fully" with the FBI, his attorney Lori Nail Basham told the Northeastern Mississippi Daily Journal. Dutschke has not been charged in the ricin case, she said.

Basham said Dutschke and Curtis were acquaintances and believed the two men had known each other for several years.

Deborah Madden, an FBI spokeswoman in Jackson, Mississippi, declined to comment. Phone calls to a number listed for Dutschke and his attorney went unanswered.

In 2007, Dutschke ran unsuccessfully as a Republican candidate against Stephen Holland, an incumbent Democratic state representative from the Tupelo area. Holland's mother, Sadie, is the judge to whom one of the ricin-tainted letters was mailed this month.

During the state campaign Dutschke produced a video titled "The Aliens are Coming," attacking his opponent for being soft on immigration, which stated that Holland was a "friend" of the September 11 hijackers.

LAWYER SAYS CURTIS WAS FRAMED

Christi McCoy, Curtis's attorney, told CNN she believed her client had been framed.

"I do believe that someone who was familiar and is familiar with Kevin just simply took his personal information and did this to him," McCoy told CNN. "It is absolutely horrific that someone would do this."

Curtis was arrested on April 17 at his home in Corinth, Mississippi. He was charged with mailing letters to Obama, Republican US Senator Roger Wicker of Mississippi and Sadie Holland containing a substance that preliminarily tested positive for ricin, a highly lethal poison made from castor beans.

The letters were intercepted by authorities before they reached their destinations. The poison scare put Washington on edge during the same week the Boston Marathon bombing occurred.

Over the weekend, investigators searched Curtis's home, his vehicle and his ex-wife's home, but failed to find any incriminating evidence, McCoy told the Northeast Mississippi Daily Journal.

In a statement last week, Curtis's family said they had not been shown any evidence of the charges against him. They said he suffers from a long history of mental illness.

Typewritten on yellow paper, the three letters contained the same eight-line message, according to an affidavit from the FBI and the Secret Service filed in court.

"Maybe I have your attention now / Even if that means someone must die," the letters read in part, according to the affidavit. The letters ended: "I am KC and I approve this message."

The initials "KC" led law enforcement officials to ask Wicker's staff if they were aware of any constituents with those initials, and the focus of the investigation then turned to Curtis, the affidavit said.

Also on Tuesday, a Pentagon spy agency said tests found no suspicious letters after an alert during a screening of incoming mail at a military base in Washington, DC.

Earlier on Tuesday, the Defense Intelligence Agency had said security personnel detected a potentially harmful substance during routine screening of incoming mail at Joint Base Anacostia-Bolling in Washington, and initial tests indicated the presence of "possible biological toxins." – Reuters