Published: Apr 23, 2013 12:43 PM EDT

OXFORD, Miss. (AP) - Officials cancelled a hearing on Tuesday for the Mississippi man accused of mailing poisoned letters to President Barack Obama, a U.S. senator and a local judge, and a news conference was planned for the afternoon.
    
Federal authorities and defense attorneys will speak to reporters at 5 p.m. CDT about the case, said Christi McCoy, the defense attorney for suspect Paul Kevin Curtis. The reason for the change in plans wasn't immediately clear.
    
The announcement came 90 minutes after the third day of the detention and preliminary hearing was supposed to start in federal court. Lawyers spent that time conferring with the judge. Later, Curtis and family members were escorted into a meeting room with his lawyers, followed by a probation officer.
    
FBI spokeswoman Deborah Madden referred questions to the U.S. attorney's office.
    
On Monday, FBI Agent Brandon Grant testified that Friday searches of Curtis' vehicle and house in Corinth, Miss., found no ricin, ingredients for the poison, or devices used to make it. A search of Curtis' computers found no evidence he researched making ricin.
    
"There was no apparent ricin, castor beans or any material there that could be used for the manufacturing, like a blender or something," Grant testified. He speculated that Curtis could have thrown away the processor.
    
Through McCoy, Curtis has denied involvement in letters containing ricin sent to Obama, Mississippi Republican Sen. Roger Wicker, and a Lee County, Miss., judge. The first of the letters was found April 15.
    
"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.
    
McCoy also questioned why Curtis would have signed the letters "I am KC and I approve this message," a phrase he had used on his Facebook page.
    
McCoy said in court that someone may have framed Curtis, suggesting that a former business associate of Curtis' brother, a man with whom Curtis had an extended exchange of angry emails, may have set him up.
    
Still, Grant testified that authorities believe they have the right suspect.
    
"Given the right mindset and the Internet and the acquisition of material, other people could be involved. However, given information right now, we believe we have the right individual," he said.
    
Grant said lab analysis shows the poison in the letters was in a crude form that could have been created by grinding castor beans in a food processor or coffee grinder.
    
Grant testified Friday that authorities tried to track down the sender of the letters by using a list of Wicker's constituents with the initials KC, the same initials in the letters. Grant said the list was whittled from thousands to about 100 when investigators isolated the ones who lived in an area that would have a Memphis, Tenn., postmark, which includes many places in north Mississippi. He said Wicker's staff recognized Curtis as someone who had written the senator before.
    
All the envelopes and stamps were self-adhesive, Grant said Monday, meaning they won't yield DNA evidence. He said thus far the envelopes and letters haven't yielded any fingerprints.
    
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