Your thinking is right on! Good work.
BA, did you read this?
Here's a much earlier story describing the CDC sending this guy into the building inadequately protected:
http://www.ph.ucla.edu/epi/bioter/testingnotdetectanthrax.html
The mysterious case of William R. Paliscak Jr. raises the troubling possibility that officials may not have fully recognized the extent of the wave of anthrax cases linked to letters sent last fall by an unidentified bioterrorist.