A police officer who went to a motel room where a large quantity of ricin was later found has tested positive for trace amounts of a substance that can be derived from the poison's source, authorities said Thursday.

"We did have one sample that had trace detectible levels of ricinine," said Pat Armour, manager of the Southern Nevada Public Health Laboratory, the local coordinator of sampling in the ricin case.

The male officer has shown no signs of illness or symptoms of ricin poisoning, officials familiar with the investigation told The Associated Press. The officials spoke on condition of anonymity, citing the ongoing investigation into the discovery of the vials of ricin and the raw material, castor beans, in the motel room.

KTNV-TV in Las Vegas identified the officer as Jim Mitchell, and aired an interview with his wife, Regina Mitchell. She said she was concerned about the test result.

About 5 percent of the U.S. population is believed to have trace detectible levels of ricinine in their system, Armour told the AP. She said it's not dangerous at that level, and it was possible the officer's urine test results stemmed from exposure to castor oil, cosmetics, particle board, paints or other manufactured products derived from castor beans.

Armour said ricinine does not derive directly from ricin, a substance for which the only legal use is cancer research. Ricinine is an alkaloid extracted from the seeds of the castor plant.

"My reports are saying 'trace detectable levels,"' Armour said. "That would be consistent with background levels of exposure to castor bean products."

It was not immediately clear that effect the officer's ricinine test had on the investigation. Las Vegas police Officer Martin Wright declined comment about the investigation or the identity of the officer.

An FBI spokesman said the officer was the only person involved in the case to have tested positive for ricinine.

Officials have said they found no actual ricin contamination in the motel room or elsewhere, and have said they could not say conclusively that the man who lived in the room, Roger Bergendorff, was poisoned.

"Beyond the possibility of Mr. Bergendorff, we are not aware of anyone else who has become ill as a result of ricin exposure from this matter," said Special Agent Joseph Dickey, a spokesman for the FBI office in Las Vegas.

Bergendorff, 57, an unemployed graphic artist, summoned an ambulance Feb. 14, complaining of respiratory distress. He spent almost four weeks in a coma and unconscious, and has been treated for kidney failure.

He remained in fair condition Thursday at a Las Vegas hospital.

Authorities suspect he was exposed to ricin, which can be lethal in amounts as small as the size of the head of a pin. But the ricin wasn't discovered until two weeks later, when a cousin went to Bergendorff's motel room to pick up his belongings. By then, the poison could have been undetectable in Bergendorff's system, authorities have said.

In court documents, police said "a large quantity" of ricin was found in vials in Bergendorff's hotel room on Feb. 28. Police said they also found firearms, along with castor beans — from which ricin is derived — and four "anarchists cookbooks" marked at sections describing how to make ricin.

FBI and police investigators questioned Bergendorff at the hospital after he regained consciousness March 12, but have not said what he told them.

Bergendorff told his younger brother he believed he had been exposed to the ricin powder. But he also told family members he had no intention of hurting anyone, and that he had the deadly poison for "self-defense."

Authorities have refused to say whether they plan to charge Bergendorff with state or federal crimes.

Ricin is categorized as a biological agent under the federal Biological Weapons Anti-Terrorism Act of 1989, which provides for the possibility of life in prison and unspecified fines for production, acquisition or possession of it.

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