"We are taking all the precautions necessary to ensure public safety," FBI agent Timothy Fuhrman said at a news conference Sunday.
Nearby homes were evacuated as FBI agents, covered from head to toe in full hazardous-material protection suits, meticulously searched the home belonging to Von Bergendorff's cousin Thomas Tholan.
Von Bergendorff had been staying in the motel room where the ricin was found and has been hospitalized since Feb. 14. Von Bergendorff has been unconscious, so police and the FBI have not been able to question him about the ricin found in his room.
Health officials are still trying to confirm whether Von Bergendorff's respiratory ailment stemmed from ricin exposure.
The FBI got a search warrant for Tholan's home, where Von Bergendorff once lived. The search began Sunday morning and continued into the afternoon.
Fuhrman said it would be a long process because agents were potentially dealing with such a toxic substance. He would not say whether the FBI suspected that Von Bergendorff had manufactured or stored ricin in the home or the rented storage units.
Residents from three surrounding homes were allowed to return by Sunday afternoon, but the Tholan house was still closed off as the search continued.
Las Vegas police said that firearms, an "anarchist-type textbook" and castor beans, from which ricin is made, were found in the room where the poison was discovered. The book was tabbed at a spot containing information about ricin.
Fuhrman said investigators were still trying to figure out why Von Bergendorff would have ricin but said there was no indication of any terrorist activity.
Neighbors say Von Bergendorff lived in the Tholan home for about a year before moving to Las Vegas about a year ago.
Police and health officials have tried to assure Las Vegas residents there is no public health threat. There was no indication of any spread of the deadly substance, they said.
As little as 500 micrograms of ricin, about the size of the head of a pin, can kill a human, according to the Centers for Disease Control and Prevention. The only legal use for ricin is cancer research.
