"He's a cousin, and he's holding his own," Tholen, 53, of Riverton, Utah, said in a brief telephone interview.
Police, the FBI and homeland security officials were trying to piece together how several vials of ricin - a rare, deadly poison with no antidote - ended up at the motel several blocks off the Las Vegas Strip.
Adding to the mystery, police said late Friday that firearms, an "anarchist-type textbook" and castor beans, from which ricin is made, were found in the room where the poison was discovered.
However, police and health officials have insisted there was no apparent link to terrorist activity. They also say there is no indication of any spread of the deadly substance beyond the vials, which three tests confirmed contained ricin. Authorities have not said how much ricin was involved but expressed confidence they have it all.
"The only positive tests (were) on the powder in question" in the vials, police Capt. Joseph Lombardo said late Friday.
The firearms and the book, which was tabbed at a spot containing information about ricin, were seized Tuesday after a manager at the Extended Stay America motel found the weapons and called police, Lombardo said. He did not elaborate.
Sgt. John Loretto, a police spokesman, said Saturday that the department was not immediately releasing more information.
Tholen took the vials to the motel office in a plastic bag while retrieving Von Bergendorff's belongings from the motel room, authorities said.
Police previously said tests did not detect the material in the motel office, the room where Von Bergendorff, 57, stayed, or a room at the Excalibur hotel-casino where Tholen stayed Wednesday night.
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.
Dr. Lawrence Sands, chief health officer of the Southern Nevada Health District in Las Vegas, said Saturday that authorities do not believe the Las Vegas public was at risk from ricin poisoning.
"Right now, we don't have any indication anyone has been exposed to ricin in the community," Sands said, adding that health officials were still trying to confirm whether Von Bergendorff's respiratory ailment stemmed from ricin exposure.
Las Vegas police, who have refused to identify Von Bergendorff or Tholen by name, said Friday that the hospitalized man was unconscious and that investigators had been unable to speak with him.
They have said Tholen arrived in Las Vegas after Von Bergendorff summoned an ambulance and was hospitalized Feb. 14 in critical condition.
Tholen contacted motel management Feb. 22 to inform them about pets in the room, and Las Vegas Humane Society officials took custody of a dog and two cats. The dog, which officials said was mortally ill after going at least a week without food or water, was euthanized.
After the vials were taken to the motel office, Tholen and six other people, including the motel manager, two motel employees and three police officers, were decontaminated at the scene and taken to hospitals for examination. None have shown any signs of being affected by ricin, officials said.
Associated Press writers Kathleen Hennessey in Las Vegas and Martin Griffith in Reno contributed to this report.