A police officer who went to a motel room where ricin was later found tested positive for trace amounts of a substance that is also derived from castor beans, the raw material for the poison, 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.

Officials familiar with the investigation told The Associated Press that the male officer, whose name and age were not made public, has shown no signs of illness or symptoms of ricin poisoning.

About 5 percent of the U.S. population is believed to have similar trace detectible levels of ricinine in their system, Armour said. She said it's not dangerous, 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.

Armor said ricinine does not derive directly from ricin.

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

Las Vegas police did not immediately respond to requests for comment.

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 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 his motel room to pick up his belongings. By then, the poison could have been undetectable in Bergendorff's system, authorities have said.