Six of the first eight tests conducted on the powder Monday showed that the substance could be ricin, a colorless, odorless poison that can be readily distilled in small quantities from castor beans and which has no known antidote. But false positives are not uncommon with ricin, according to experts, and a sample arrived Tuesday morning at Fort Detrick, Md., where the army has an advanced laboratory for testing.
"We haven't finished any testing," said Fort Detrick spokesman Chuck Dasey. Dasey said the lab will release the test results to the Department of Homeland Security probably no earlier than the end of the day Tuesday.