Just days after anti-terrorist police found small amounts of ricin in a London apartment, the FBI has issued a special bulletin alerting US police to the dangers of the deadly toxin.
In a special edition of the FBI Intelligence Bulletin sent out to 17,000 law enforcement officials across the country, the agency gave a detailed explanation of the potential effects of the toxin and how to handle ricin, which could be used in a bio-warfare attack.
"Use of ricin toxin as a weapon would be most effective in an assassination by injection or as a food contaminant," the bulletin said.
"Ricin could be used in a terrorist operation to contaminate closed ventilation systems (e.g. heaters or air conditioners), drinking water, lakes, rivers and food supplies," it said.
Derived from the beans of the castor plant, ricin is a natural occurring chemical that can be easily produced and could potentially be used as a weapon of mass destruction.
Small amounts of ricin found in London sparked action by law enforcement agencies in Britain and around the world.
The bulletin said US experts believe ricin is ineffective as an aerosol-based weapon.
The FBI said ricin it should only be handled by trained hazardous materials professionals.
There have been a small number of cases in the United States that involved the use or near-use of ricin, the bulletin said.
In April, 1991 several members of a domestic extremist group called the Patriot's Council in Minnesota manufactured ricin from castor beans and discussed using it against federal law enforcement officers. Four men were convicted for their role in the plot.
The amount of the toxin produced then could have killed more than 100 people if effectively delivered, the FBI bulletin said.