A federal law-enforcement official, who asked for anonymity when discussing sensitive information, said that the U.S. Marshals Service—which is responsible for courthouse security and transporting federal prisoners—has been working “for months” on security measures for possible trials of accused 9/11 perpetrators, as well as other terrorist suspects who had been held in the military prison facility in Guantánamo, Cuba, and/or in a now shuttered network of secret detention facilities maintained by the CIA. Among security measures the Marshals Service has already undertaken are assessments of the risks the presence of high-level Qaeda prisoners, such as Mohammed, would pose for New York—and what kind of bodyguard squads will be needed to guard trial participants, like judge and jury.