LAS VEGAS — An unemployed graphic designer who authorities say poisoned himself with toxic ricin in his Las Vegas motel room has pleaded guilty to possessing a biological toxin.

Sitting in a wheelchair, Roger Bergendorff was told he could spend three years and a month in federal prison. He also pleaded guilty Monday to possessing unregistered handgun silencers. A third charge was dropped.

The judge scheduled sentencing for Nov. 3.

Bergendorff, 57, had pleaded not guilty.

Trial has been set to begin Sept. 9 for the unemployed graphic designer who authorities suspect poisoned himself in his extended-stay room just off the Las Vegas Strip.

Bergendorff has been in federal custody since his arrest April 16, after two months in a Las Vegas hospital.

Authorities have said the case has no ties to terrorism but that Bergendorff admitted keeping ricin for protection against unspecified personal enemies.

Las Vegas police and federal authorities reported finding about 4 grams of "crude" powdered ricin Feb. 28 in Bergendorff's motel room, along with illegal silencers for .22-caliber weapons. Police also confiscated several how-to manuals for producing ricin, and castor beans from which the substance can be derived.

Ricin can be lethal in amounts the size of the head of a pin. A federal prosecutor told a judge he believes Bergendorff had enough of the powder to kill more than 500 people.

Bergendorff's cousin, Thomas Tholen, of Riverton, is scheduled for a change of plea hearing Monday in federal court in Salt Lake City. He originally was charged with one felony count of knowing about a crime but failing to report it.

Federal prosecutors allege Tholen knew Bergendorff made ricin in Utah before moving to Las Vegas.

Bergendorff summoned an ambulance Feb. 14, complaining of breathing trouble and also was treated for kidney failure.

Authorities said his symptoms were consistent with ricin exposure, although his attorney denied ricin made him sick. 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.