THE MAN ACCUSED of being the main plotter in the September 11 attacks in 2001 has agreed to plead guilty, the US Defence Department said.

Khalid Sheikh 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.

Pentagon officials declined to immediately release the terms of the plea bargain. The New York Times, citing unidentified Pentagon officials, said the terms included the men’s longstanding condition that they be spared risk of the death penalty.

Defence 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 September 11.

The US agreement with the men to enter into a plea agreement comes more than 16 years after their prosecution began for the attack, and over 20 years after militants flew commandeered commercial airliners into buildings.

The attack killed nearly 3,000 people and triggered years of US wars against militant extremist groups that reshaped Middle Eastern countries.

Terry Strada, national chairperson of 9/11 Families United, a group of families of victims, had been at Manhattan federal court for a hearing on one of many civil lawsuits when she heard news of the plea agreement.

She said many families just wanted to see the men admit guilt.

“For me personally, I wanted to see a trial,” she said. “And they just took away the justice I was expecting, a trial and the punishment.

“They were cowards when they planned the attack. And they’re cowards today.”

Dozens of relatives of those killed have died while awaiting resolution of the case, Ms Strada added.

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

Mohammed was captured in 2003. He was subjected to waterboarding 183 times while in CIA custody before coming to Guantanamo, along with other torture and coercive questioning.

The use of torture has proven one of the most formidable obstacles in US efforts to try the men in the military commission at Guantanamo, owing to the inadmissibility of evidence linked to abuse.

Torture has accounted for much of the delay of the proceedings, along with the courtroom’s location a plane ride away from the United States.

Michael Burke, one of the family members receiving the government notice of the plea bargain, condemned the long wait for justice, and the outcome.

“It took months or a year at the Nuremberg trials,” said Mr Burke, whose fire captain brother Billy died in the collapse of the World Trade Centre’s North Tower.

“To me, it always been disgraceful that these guys, 23 years later, have not been convicted and punished for their attacks, or the crime. I never understood how it took so long.

“I think people would be shocked if you could go back in time and tell the people who just watched the towers go down, ‘Oh, hey, in 23 years, these guys who are responsible for this crime we just witnessed are going to be getting plea deals so they can avoid death and serve life in prison’.”