When poison-laced letters were sent to President Barack Obama and two other officials, it didn't take long to track down a suspect based on a phrase often used by an Elvis impersonator named Kevin Curtis: "I am KC and I approve this message." Curtis was soon arrested at his house in north Mississippi and charged in the case. He swore he didn't do it, and told investigators that maybe a longtime foe, a martial arts instructor named James Everett Dutschke, might have something to do with the case. By the time Curtis was released on April 23, the FBI was already watching Dutschke. It was another twist in a plot Curtis' lawyer has called "diabolical." According to an FBI affidavit made public Tuesday, agents saw Dutschke the day before Curtis' release hauling items out of his former martial arts studio in Tupelo, Miss. Tests in the studio and on some of those items, including a dust mask, have tested positive for ricin, the same deadly substance found in the letters sent to Obama, U.S. Roger Wicker and Lee County, Miss., Judge Sadie Holland, the affidavit says. The affidavit also said numerous documents found in Dutschke's home had printer markings that were similar to ones on the letters and that he had used the Internet to buy castor beans, from which ricin is derived. Dutschke, 41, was arrested Saturday by FBI agents at his home in Tupelo, and is being held without bond pending a preliminary and detention hearing Thursday in U.S. District Court in Oxford, Miss. Annette Dobbs, who owns the small shopping center where the studio was located, said authorities padlocked the door to it last week. They also searched his house and vehicles. Dobbs said Tuesday that FBI agents haven't told her anything, including whether the building poses a health threat. Police tape covered the front and the small back door. An expert at the National Bioforensics Analysis Center in Fort Detrick, Md., said the extraction process employed in this case appears to have been more involved than "merely grinding castor beans," the affidavit said. Dutschke bought 50 castor beans off eBay in November 2012 and 50 more in December 2012, the affidavit said.