Ricin was found in the former martial arts studio of the man suspected of sending poison letters to President Barack Obama and other public officials, and was also discovered on a dust mask and other items he threw in the trash, federal prosecutors said in a court document made public Tuesday.

The affidavit says an FBI surveillance team saw James Everett Dutschke remove several items from the studio in Tupelo, Miss., on April 22 and dump them in a trash bin about 100 yards down the street. The items included a dust mask that later tested positive for ricin, the affidavit said.

Traces of ricin also were found in the studio and Dutschke used the Internet to buy castor beans, from which ricin is derived, the affidavit said.

Annette Dobbs, who owns the small shopping center where the studio was located, said authorities padlocked the door to it sometime during the search. She said Tuesday that FBI agents haven’t told her anything, including whether the building poses a health threat. Inside the studio is one large room with a smaller reception area and a concrete floor. Police tape covered the front and the small back door.

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.

The FBI searched his home, vehicles and studio last week, often while wearing hazardous materials suits. Attention turned to Dutschke after prosecutors dropped charges against an Elvis impersonator who says he had feuded with Dutschke in the past.

Dutschke said last week that he didn’t send the letters. His lawyer, federal public defender George Lucas, had no comment Tuesday about the information in the affidavit.

Dutschke was arrested as part of the investigation into poison-tainted letters sent to Obama, U.S. Sen. Roger Wicker and Lee County, Miss., Judge Sadie Holland.

The FBI has not yet revealed details about how lethal the ricin was. A Senate official has said the ricin was not weaponized, meaning it wasn’t in a form that could easily enter the body. If inhaled, ricin can cause respiratory failure, among other symptoms. No antidote exists.

Dutschke also bought 50 castor beans off eBay in November 2012 and 50 more in December 2012, the affidavit said.

The affidavit had been sealed since it was filed Friday in U.S. District Court in Oxford. It also said that on the evening of Dec. 31, 2012, someone using his “computer downloaded a publication, ‘Standard Operating Procedure for Ricin,’ which describes safe handling and storage methods for ricin, and approximately two hours later, ‘Immunochromotography Detection of Ricin in Environmental and Biological Samples,’ which describes a method for detecting ricin.”

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.

A witness, who is not named in the document, told investigators that Dutschke once said years ago that he knows how to make poison that could be sent to elected officials and “whoever opened these envelopes containing the poison would die.”

The first suspect accused by the FBI, Paul Kevin Curtis, 45, was arrested on April 17 at his Corinth, Miss., home, but the charges were dropped six days later. After his arrest, Curtis said he was framed and gave investigators Dutschke’s name as someone who could have sent the letters, the affidavit said.