GUANTANAMO BAY, Cuba — Khalid Sheikh Mohammed, the mastermind of 9/11, appeared inside Guantanamo Bay’s war court for the first time in more than 500 days on Tuesday following another massive delay in the case due to COVID-19.

Mohammed, dubbed “KSM” and described as “the principal architect of the 9/11 attacks” in the 9/11 Commission Report, and some of his co-defendants were smiling and bantering with each other and their lawyers, with KSM briefly waving to the gallery.