Media playback is unsupported on your device Media caption Paul Curtis: ''I respect President Obama and I love my country''

US authorities have dropped the charges against a Mississippi man accused of sending letters poisoned with ricin to President Barack Obama and a senator.

Paul Curtis was freed on Tuesday after prosecutors revealed the investigation had uncovered "new information".

The letters addressed to the president and a Mississippi senator tested positive for the presence of the lethal toxin this month.

Meanwhile, investigators in the case are searching the home of another man.

Mr Curtis was arrested last week at his home in the town of Corinth, Mississippi and charged with sending letters to Mr Obama, Republican Mississippi Senator Roger Wicker and a judge from Lee County.

'Very diabolical'

But on Monday authorities searched Mr Curtis' home and found neither ricin nor ingredients for the poison, an FBI agent testified in court. A search of his computer yielded no evidence he had researched how to make the toxin, the agent said.

Ricin Can be fatal when inhaled, ingested or - most dangerously - injected

One to three castor beans chewed by a child, or just eight seeds chewed by an adult, can be fatal

The toxin is part of the waste produced when castor oil is made Q&A: What is ricin?

In a news conference outside the courthouse on Tuesday, Mr Curtis thanked his family, friends, Jesus, Sen Wicker and Mr Obama.

Referring to investigators' questions, he said: "I thought they said rice and I said, 'I don't even eat rice.'

Mr Curtis, a musician and Elvis impersonator who also said he was a certified reflexologist, added: "I love my country and would never do anything to pose a threat to [Mr Obama] or any other US official.

"I would like to get back to normal, which for me means being the best father that I could be for my children and entertaining through my music."

He was already well known to Sen Wicker because he had written to the Republican senator and other officials.

Mr Curtis' lawyer Christi McCoy, whom Mr Curtis described as a blonde, blue-eyed angel sent by God, told reporters she believed the FBI agents who had arrested and charged her client had "acted in good faith".

Ms McCoy said she was unsure what new information prosecutors had but that the plot to frame her client was "very, very diabolical".

According to an FBI affidavit released on Thursday, the letters read: "Maybe I have your attention now even if that means someone must die. To see a wrong and not expose it, is to become a silent partner to its continuance."

The letters were signed: "I am KC and I approve this message."

Mensa dispute

As the case against Mr Curtis appeared to collapse on Monday and Tuesday, another man in nearby Tupelo, Mississippi, told the Associated Press authorities were searching his home in connection with the ricin letters.

Image caption Everett Dutschke denies sending the poisoned letter

Everett Dutschke said he was innocent, and the Associated Press reported agents from numerous law enforcement agencies had established a mobile crime lab near his home.

"I don't know how much more of this I can take," Mr Dutschke said. No charges have been filed against him nor has he been arrested.

The search team also combed through an area of woods and ditches about a block from Mr Dutschke's property.

Mr Dutschke said he and Mr Curtis had had a dispute, cutting off contact in 2010, after he threatened to sue Mr Curtis for saying he was a member of Mensa, a group for people with high IQs.

"I'm a patriotic American," Mr Dutschke, who unsuccessfully ran for a seat in the Mississippi House of Representative in 2007, said. "I don't have any grudges against anybody. I did not send the letter."

Ricin, extracted from castor beans, is 1,000 times more toxic than cyanide.

It can be fatal when inhaled, swallowed or injected, although it is possible to recover from exposure.