Sometime in February or March, officials at the Justice Department held a closed-door meeting with a federal judge in Washington, where they laid out what the government knows about the anthrax-letter attacks of 2001. Nobody is exactly sure what the department told the judge during that meeting. People familiar with the presentation say it was held under top-secret conditions; documents were escorted to the courtroom under the supervision of the U.S. Marshals Service, and the judge was not even allowed to keep copies of the papers that were shown to him. But at a hearing on March 29, the judge,...