(Greenville-AP) Feb. 3, 2004 - Investigators sent out hundreds of thousands of fliers to Upstate residents as they try to find who is responsible for a sending vial of the deadly poison ricin to a post office in Greenville last fall.

Federal investigators say a substance found Monday night in US Senate offices has positively tested as Ricin.

Investigators think the person who sent the package is familiar with the area, because the post office where it was found is not used by the general public. The facility serves the Greenville-Spartanburg International Airport.

The package was delivered to the facility on October 15th and contained a letter with a threat to start dumping ricin into drinking reservoirs around the country if new federal trucking regulations requiring drivers to rest longer weren't repealed.

The rules, which started on January 4th, are intended to increase safety by making truckers rest more. Drivers now must get eight hours rest and can work 15 hours, ten of which can be on the road; one more hour on the road, one less hour work and two more hours of rest.

Officials would not say to whom the envelope was addressed or where it was postmarked. No one was hurt by the poison.

According to the Centers for Disease Control and Prevention, ricin is made from the waste left over from processing castor beans. The CDC says people can breathe in ricin mist or powder and be poisoned.

Depending on the type of exposure, such as injection, the CDC says as little as 500 micrograms of ricin could be enough to kill an adult. That dose would be about the size of the head of a pin.

It can cause fever, cough and chest tightness within eight hours after being ingested or inhaled. Death can come between 36 and 72 hours after exposure. There is no antidote.

posted 8:42am by Chris Rees