[Don Myers]

Supposedly, the powder has to pass three separate tests to be conclusively anthrax. Then they said it was positive for the first test and negative for the second test. Then they said the last test would determine if it was anthrax. If it has to pass all three tests, I don't know how the last test will be conclusive since the powder failed the second test.

[meyer]

Its probably a lot like a drug test. It goes through a cheap, dirty initial test first which isn't real accurate. Any positives are then tested further and in greater depth using a more expensive but more accurate test. It makes sense.