He is charged with possession of a biological toxin and two weapons offenses stemming from materials authorities said were found Feb. 26 and Feb. 28 in his room at an extended-stay motel several blocks off the Las Vegas Strip.
Speaking from a wheelchair, Bergendorff told a federal judge in his initial court appearance that it was "not in my blood" to use the deadly poison.
"I didn't use that stuff," Bergendorff said as his court-appointed lawyer advised him not to say more, "because I couldn't."
The charges carry a possible penalty of 30 years in federal prison and a $750,000 fine. The judge ordered that Bergendorff, 57, remain in custody until a preliminary hearing May 2.
Prosecutors said in a six-page complaint that Bergendorff told investigators he first made ricin in San Diego in the late 1990s, and later made the substance while living in Reno and in the basement of his cousin's house in Riverton, Utah.
The complaint said that a June 2002 receipt for castor bean seed, purchased from a Michigan company, was found in an Utah storage locker rented by Bergendorff. The listed purchaser, "Roger's Patio and Garden," was apparently a fictitious business created by Bergendorff, the complaint said.
Cancer research is the only legal use for ricin, which has no antidote and can be lethal in amounts the size of the head of a pin.
Authorities do not allege Bergendorff's possession of ricin had anything to do with terrorism, according to court documents.
"Bergendorff characterized the production of ricin as an 'exotic idea,'" the complaint said.
Over the course of several interviews with the FBI, "Bergendorff admitted that there have been people who have made him mad over the years and he had thoughts about causing them harm to the point of making some plans," the complaint said. "However, he maintained that he never acted on those thoughts or plans."
Bergendorff and his lawyer, Paul Riddle, acknowledged the seriousness of the charges, which carry a possible penalty of 30 years in federal prison and a $750,000 fine.
Officials say Bergendorff's symptoms were consistent with ricin exposure, but it may never be certain that the toxin sickened him because all traces of the substance are eliminated from the body within days, and the ricin in his motel room was found well after he got sick.
Riddle denied Bergendorff was sickened by ricin.
"His poor health is not a result of exposure to ricin," Riddle told the judge. He said Bergendorff fell ill in February with pneumonia and kidney failure, resulting from a mental and emotional downturn after his older brother died in January.
Bergendorff's cousin Thomas Tholen, 54, was charged this month in Salt Lake City with misprision of felony, which means failing to report a crime.
The complaint said Tholen told investigators that Bergendorff had talked to him about how easy it would be to make ricin, and that Bergendorff showed him a vial or beaker with a powder he believed to be ricin in December 2005.
Tholen declined to comment when reached by telephone Wednesday. His lawyer Greg Skordas denied Tholen knew Bergendorff had ricin.
"Tom always maintained that he was unaware of Bergendorff ever producing or possessing or manufacturing ricin while they were together," Skordas said.
Roger Bergendorff's brother, Erich Bergendorff, said he spoke with him Tuesday by telephone.
"He just said he wasn't going to face charges, but I don't think that was based on fact," said Erich Bergendorff, who lives in Escondido, Calif. "It's my impression that he didn't understand the hazard he posed."
Bergendorff, who lived with his dog and two cats, summoned an ambulance to his Las Vegas motel room Feb. 14, complaining of respiratory distress. He spent almost four weeks unconscious at a Las Vegas hospital. Family members said he also was treated for kidney failure.
Tholen was collecting Bergendorff's belongings from the motel room Feb. 28 when he gave a motel manager a plastic bag containing several vials of what turned out to be ricin powder.
The complaint refers to the substance as "crude" and 2.9 percent "active ricin."
"That's not pure," said Andrew Ternay Jr., founder of the Rocky Mountain Center for Homeland Defense at the University of Denver and author of "The Language of Nightmares," a glossary of terms for chemical, biological and nuclear weapons.
"But it is deadly no matter," Ternay said. "It's just that it would take more to kill someone."
Police and homeland security officials have said they found no ricin contamination in any place Bergendorff stayed.
U.S. Attorney Gregory Brower said the charges of possession of unregistered firearms and possession of firearms not identified by serial number stemmed from the seizure by Las Vegas police of two .25-caliber pistols, a .22-caliber Ruger rifle and a .22-caliber Browning pistol with a silencer.