As police tried to piece together how a rare, fatal poison ended up in a motel for transients, the 57-year-old man who could hold the key lay unconscious in a Las Vegas hospital room.

Adding to the mystery, police said that firearms and an "anarchist-type textbook" were found in the same room the ricin was found — two days before vials of the substance were discovered Thursday.

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Capt. Joseph Lombardo said at a press conference late Friday that the book was tabbed at a spot with information about ricin. Police found the weapons and books on Tuesday, after a manager at the Extended Stay America motel called police upon finding weapons, he said.

After authorities seized the book and weapons, tests for ricin were conducted but were negative, said Lombardo.

Lombardo said a 53-year-old friend or relative of the sick man made contact with motel management on Feb. 22 to inform them about pets in the room — a dog and two cats.

Click here to read Adam Housley's blog on the case.

Earlier Friday, police Deputy Chief Kathy Suey said that the friend or relative found the vials after going to the motel to retrieve the hospitalized man's belongings, and brought them to the apartment manager. Authorities confirmed Friday the vials contained ricin.

It was unclear how long the vials were in the unoccupied motel room, and whether they might have been overlooked when ricin tests were conducted on Tuesday.

Lombardo did not address such questions during the brief news conference.

"The only positive tests was on the powder in question" in the vials, said Lombardo.

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Authorities have repeatedly said there was no apparent link to terrorist activity, and no indication of any spread of the deadly substance beyond the vials.

The 57-year-old man was the last to stay in the room, and was in critical condition since calling an ambulance on Feb. 14 complaining of respiratory distress.

Authorities offered little more about the hospitalized man's identity: he left pets in the room and was not considered a suspect. A dog was found dead but the animal had gone at least a week without food or water, Suey said.

"We don't know an awful lot about him," Suey said. "We don't even know that it was him that was in possession of the ricin." She said she could not say how much ricin was in the vials.

Lombardo said precautionary tests were also done in a room at the Excalibur hotel-casino, on the Las Vegas Strip, where the friend or relative had been saying. He said they were negative.

Authorities have also not released more information about the friend or relative.

The only legal use for ricin is cancer research. A pinprick of ricin is enough to kill.

Police, National Guard, homeland security and FBI officials responded when the substance was found Thursday.

Seven people, including the man who found the ricin, the manager, two other 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, Suey said. All have been released.

Along with the ricin, police found castor beans possibly used to make the substance. Suey said the manufacture of ricin is a crime.

Greg Evans, director of the Institute for Biosecurity at Saint Louis University in Missouri, said the man's respiratory illness suggested he was exposed to a powder fine enough to float in the air.

"If he went to the hospital with difficulty breathing, he actually inhaled it," Evans said. "For some reason he opened the vial and it must have been aerosolized."

Multiple vials would probably contain enough ricin to sicken many people if it was spread, for example, around a buffet table or sprayed in a closed room.

"If it was aerosolized in a confined space then it certainly could harm dozens of people," he said.

As little as 500 micrograms of ricin, or about the size of the head of a pin, can kill a human, according to the Centers for Disease Control and Prevention in Atlanta.

In March 2003, a Las Vegas man committed suicide by injecting himself with liquid ricin. He was a retired gaming executive and former chemist.

For the most part, however, the toxin has more of a cloak-and-dagger reputation linked more closely to spies and assassins.