The man accused of being the principal architect of al-Qaeda’s Sept. 11, 2001, attacks has agreed to plead guilty, the Defense Department announced Wednesday. Khalid Sheikh Mohammed and two accomplices involved in the attack are anticipated to enter their pleas at the military commission at Guantanamo Bay, Cuba, as early as next week. Khalid Sheikh Mohammed (KSM) is a high-ranking member of al-Qaeda and is considered the principal architect of the September 11, 2001 terrorist attacks. He was captured in Pakistan in 2003 and has been held at the Guantanamo Bay detention camp since then. Read: U…