WASHINGTON (AP) — Khalid Sheikh Mohammed, accused as the mastermind of al-Qaida’s Sept. 11, 2001, attacks on the United States, has agreed to plead guilty, the Defense Department said Wednesday. The development points to a long-delayed resolution in an attack that killed thousands and altered the course of the United States and much of the Middle East.

Mohammed and two accomplices, Walid bin Attash and Mustafa al-Hawsawi, are expected to enter the pleas at the military commission at Guantanamo Bay, Cuba, as soon as next week.

Defense lawyers have requested the men receive life sentences in exchange for the guilty pleas, according to letters from the federal government received by relatives of some of the nearly 3,000 people killed outright on the morning of Sept. 11.

Terry Strada, the head of one group of families of the nearly 3,000 direct victims of the 9/11 attacks, invoked the many relatives who have died while awaiting justice for the killings when she heard news of the plea agreement.

“They were cowards when they planned the attack,” she said of the defendants. “And they’re cowards today.”

Pentagon officials declined to immediately release the full terms of the plea bargains.

The U.S. agreement with the men comes more than 16 years after their prosecution began for al-Qaida’s attack. It comes more than 20 years after militants commandeered four commercial airliners to use as fuel-filled missiles, flying three of them into the World Trade Center in New York and the Pentagon.