"I do have the authority to impose a sentence higher or lower," U.S. District Judge Robert C. Jones said. "Do you understand?"
"Yes," Bergendorff answered in a clear and steady voice. Bergendorff pleaded guilty to possession of a biological toxin and possession of unregistered handgun silencers. A third charge of possession of firearms without serial numbers was dropped. Prosecutor Gregory Damm reiterated the case had no ties to terrorism.
Jones set sentencing for Nov. 3.
Bergendorff has been in federal custody since his arrest April 16, when he was released from a hospital after spending nearly two months unconscious and on kidney dialysis. Authorities suspect he poisoned himself in his room just off the Las Vegas Strip, and have said Bergendorff's symptoms were consistent with ricin exposure.
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.
Bergendorff's attorney, Paul Riddle, denied that ricin made his client sick.
"He still maintains that it wasn't the ricin," Riddle said Monday.
Traces of the substance are eliminated from the body within days, and ricin was not found in Bergendorff's motel room until two weeks after he went to the hospital.
Riddle said Bergendorff benefited under the plea agreement because he received credit for accepting responsibility and because the agreement included a recommended sentence.
Authorities said Bergendorff told investigators he first made ricin in San Diego in the late 1990s and later made it while living in Reno and in the basement of his cousin's house in Riverton, Utah. They said he told investigators he had made a crude powdered form of ricin and kept it in his extended-stay motel room for protection against unspecified personal enemies.
But he insisted in court in April that he never would have used it.
Bergendorff called an ambulance on Feb. 14 and complained of breathing trouble.
Two weeks later, Las Vegas police and federal authorities were given about 4 grams of ricin powder found in small plastic bags in Bergendorff's motel room, where they also found illegal silencers for .22-caliber handguns.
Damm told a judge in April that he believed Bergendorff had enough ricin powder to kill more than 500 people. Bergendorff's cousin, Thomas Tholen, of Riverton, Utah, is scheduled for a change-of-plea hearing Aug. 11, U.S. attorney's spokeswoman Melodie Rydalch said.
Tholen has pleaded not guilty to one felony count of knowing about a crime but failing to report it. Rydalch declined to describe the nature of the plea deal with Tholen.
Tholen's defense attorney, Greg Skordas, didn't immediately return a telephone message seeking comment.
Federal prosecutors allege Tholen, 54, knew Bergendorff made ricin in Utah before moving to Las Vegas.
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Associated Press writers Paul Foy in Salt Lake City and Allison Hoffman in San Diego contributed to this report.
