OXFORD, Mississippi (AP) ― A Mississippi man charged with mailing ricin-tainted letters to national leaders wrote in online postings that he had uncovered a conspiracy to sell human body parts on the black market, and on Thursday his attorney said he was surprised by his arrest and maintains he is innocent.

Paul Kevin Curtis, 45, wore shackles and a Johnny Cash T-shirt Thursday in a federal courtroom. His handcuffs were taken off for the brief hearing, and he said little. He faces two charges on accusations of threatening President Barack Obama and others. If convicted, he could face up to 15 years in prison.

He did not enter a plea on the two charges. The judge said a preliminary hearing and a detention hearing are scheduled for 3 p.m. Friday.

Attorney Christi R. McCoy said Curtis “maintains 100 percent that he did not do this.”

“I know Kevin, I know his family,” she said. “This is a huge shock.”

McCoy said she has not yet decided whether to seek a hearing to determine whether Curtis is mentally competent to stand trial.

Curtis, who was arrested Wednesday at his home in Corinth, near the Tennessee state line, was being held in the Lafayette County jail in Oxford, Mississippi.

An FBI affidavit says Curtis sent three letters with ricin to Obama, U.S. Sen. Roger Wicker and a Mississippi judge. The letters read:

“No one wanted to listen to me before. There are still ‘Missing Pieces.’ Maybe I have your attention now even if that means someone must die. This must stop. To see a wrong and not expose it, is to become a silent partner to its continuance. I am KC and I approve this message.”

The affidavit says Curtis had sent letters to Wicker’s office several times before with the message, “this is Kevin Curtis and I approve this message.”

In several letters to Wicker and other officials, Curtis said he was writing a novel about black market body parts called “Missing Pieces.”