The FBI has released Paul Kevin Curtis, who they suspected had sent letters containing ricin to President Obama and a senator last week, and dropped all charges against him. They are still searching for the culprit. NBC's Andrea Mitchell reports.

Charges were dropped Tuesday against the Mississippi man suspected of mailing ricin-laced letters to President Obama and other public officials — as authorities searched the home of another man hoping to find clues in the expanding investigation.

"I respect President Obama and love my country. I would never do anything to pose a threat to him or any other U.S. official," Paul Kevin Curtis said at a news conference Tuesday.

AP Paul Kevin Curtis

Curtis was arrested last Wednesday at his home in Corinth, Miss. Two letters that initially tested positive for ricin, a poison, had been found earlier in the week -- one addressed to Sen. Roger Wicker, R-Miss., and one to President Obama.

"This past week has been a nightmare for myself and my family. My mother has suffered, as well as my children. I would like to get back to normal, which for me means being the best father I can to my children," he said.

Hours after Curtis' release, authorities searched the home of another Mississippi man, J. Everett Dutschke, as part of the investigation, reported WTVA. Dutschke's name had come up earlier this week when Curtis' defense attorney Christi McCoy suggested prosecutors look into him, though on Tuesday she shied from any suggestion that Dutschke was the one responsible for the letters.

The two men have a history of menacing communications, which Curtis detailed during the press conference.

On the day his home was being search, Dutschke told the Jackson Clarion Ledger, “I guess Kevin got desperate. I feel like he’s getting away with the perfect crime.”

According to an FBI bulletin, both letters were postmarked April 8, 2013, out of Memphis, Tenn., and included an identical phrase: "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." It is a sign off phrase Curtis used frequently in Internet postings.

Another suspicious letter was sent to a Lee County, Miss., judge.

On Monday, an FBI agent testified that a search of Curtis' vehicle and home did not yield any ricin or castor beans, the ingredients needed to make the poison.

"There was no apparent ricin, castor beans or any material there that could be used for the manufacturing, like a blender or something," Agent Brandon Grant said in an Oxford, Miss., courtroom, reported The Associated Press. He said there was a possibility Curtis could have thrown away the processor, and that computer technicians were taking a deeper look at Curtis' computer after an initial search didn't find documents or searches connected to ricin.

McCoy argued on Monday that the government does not have probable cause to hold Curtis, an Elvis impersonator who relatives say has bipolar disorder.

"The searches are concluded, not one single shred of evidence was found to indicate Kevin could have done this," McCoy told reporters after the hearing Monday.

Also on Tuesday, Senate Majority Leader Harry Reid set off a new round of concerns after telling reporters ricin had been found at a mail facility at Joint Base Anacostia-Bolling in Washington, D.C. However, the Defense Intelligence Agency later clarified in a statement that screening equipment alerted authorities to potential hazardous substance, but an investigation found no suspicious packages or letters.

The Associated Press contributed to this report.

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