Ricin has been a byword for terrorism in the mass media since Colin Powell used it to link Iraq-based terrorists to groups plotting attacks in Europe as part of the U.S. case for invasion in 2003. But the ricin in that incident turned out to be no more real than Saddam Hussein's weapons of mass destruction, and experts say that the toxin is so difficult to purify it is unlikely to ever be used successfully in a terror attack.

Samples of the substance found in a Las Vegas motel room last week after its occupant was hospitalized with breathing difficulties will be analyzed by the federal Centers for Disease Control and Prevention in Atlanta and the FBI's Hazardous Materials Response Unit, officials told United Press International Monday.

Two CDC specialists were already in Las Vegas at the request of state and local authorities, the agency's spokesman Von Roebuck told UPI. He said they were working to help ascertain what had sickened Roger Von Bergendorff, a resident at the Extended Stay America motel who was hospitalized Feb. 14 and remains in critical condition.

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Experts say that with no conclusive analysis of either the substance or the patient it is hard to tell what might have been found in Bergendorff's room, and some accuse local officials -- and the news media -- of getting out ahead of the story.

"There are field tests, but the lab testing will eliminate the possibility of a false positive," FBI spokesman Richard Kolko acknowledged.

Roebuck told UPI the agency's lab had received samples for confirmatory testing Monday but could not say when the results would be available.

Ramon Denby, a spokesman for the Las Vegas police who recovered the substance after it was handed to the motel management, told UPI a hazmat unit called the Armor Team had conducted field tests on the substance and determined that it contained ricin.

He said the tests had been "conclusively confirmed" by a U.S. military lab. "It was 100 percent positive for ricin," he said.

But a spokeswoman for the Nevada National Guard's 92nd Civilian Support Team who carried out the second set of tests told UPI the results were only preliminary and operated on the precautionary principle.

"The mobile lab rolls in when requested by law enforcement," Capt. April Conway said. "Their job is to take the first cut on what (any substance found) is. They tell the first responders, 'We think you're dealing with ricin,' or whatever it is. ¿¿ The aim is to protect first responders."

Experts say field testing only reveals the presence of ricin, a protein derived from castor beans that in its purest form is highly toxic.