Five Guantanamo Bay prisoners charged in attacks of September 11, 2001, were back in court in Cuba Monday.
Khalid Sheikh Mohammed and four co-conspirators appeared relatively calm and respectful, a sharp contrast from their behavior at their arraignment in May.
This week's pre-trial hearings will focus on security measures to protect the release of classified intelligence information.
Families of the 9/11 victims were invited to watch from military installations in New York, New Jersey, Massachusetts, and Maryland.
If convicted, the terror suspects could face the death penalty.