Once a scientist working in a US government lab is arrested, the "dirt", as you say, is already out, i.e., the US has been working on weaponized anthrax which is a treaty violation.
One of us is badly confused. I'm under the impression that the government is making no bones whatever about having done research on bioweapons, and that news articles for months have reported that they suspect the source of the postal anthrax is a disgruntled US worker who learned about the technology in US labs. I also don't think there's any treaty violation implied. What treaty do you think would be violated and why?