Roger Von Bergendorff, the focus of the investigation, had lived in the Riverton house for more than a year before moving to Las Vegas about a year ago, said Tammy Ewell, who lives across the street.
"He just barely got by in life. He'd just barely make it," Ewell said Saturday of the 57-year-old Von Bergendorff.
He lived there with his cousin Thomas Tholen and his wife, said Ewell, who described the couple as close friends.
Officials secured Tholen's home, but did not immediately search it because they were awaiting court approval for a warrant, FBI spokesman Juan Becerra said later Saturday.
In a brief telephone interview, Thomas Tholen told The Associated Press that Von Bergerdorff was "holding his own" in the hospital.
Tholen, 53, wouldn't say much more about his cousin or the discovery Thursday of several vials of ricin - which is deadly in minuscule amounts - at Von Bergendorff's extended-stay motel room on the Las Vegas Strip.
Authorities have not said how much ricin was involved but expressed confidence they have seized all of it.
Health officials were still trying to confirm whether Von Bergendorff's respiratory ailment stemmed from ricin exposure.
Police and health officials have tried to assure Las Vegas residents there is no public health threat. There was no apparent link to terrorist activity and no indication of any spread of the deadly substance, they said.
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.
The firearms and the book, which was tabbed at a spot containing information about ricin, were seized Tuesday, police Capt. Joseph Lombardo said. He did not elaborate.
Ewell, the Tholens' neighbor, said Von Bergendorff was a "loner" and that she often saw him walking his German shepherd on the street. It wasn't clear what he did for a living or how he spent his time.
Toward the end of his stay, he started attending the local Mormon church and briefly moved out of the Tholen home into a neighbor's camper, she said.
Tholen is a former high school art teacher who now sells insurance with his wife, she said.
"The Tholens were the last ones we'd expect anything to happen to," Ewell said.
Tholen went to Von Bergendorff's Las Vegas motel room on Feb. 22 and took the vials to the motel office in a plastic bag while retrieving his cousin's belongings, authorities said.
Police previously said tests did not detect the material in the motel office, the room where Von Bergendorff stayed, or a room at the Excalibur hotel-casino where Tholen stayed Wednesday night.
After the vials were taken to the motel office, Tholen and six other people were decontaminated at the scene and taken to hospitals for examination. None have shown any signs of being affected by ricin, officials 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.
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.