The three include Khalid Sheikh Mohammed, who is accused of masterminding the attacks that killed nearly 3,000 people.

The United States has announced plea agreements with three men held in Guantanamo and accused of plotting the September 11, 2001, attacks, including alleged mastermind Khalid Sheikh Mohammed.

The Pentagon did not release full details of the deals involving Mohammed, Walid bin Attash, and Mustafa al-Hawsawi, but US media reported the three would plead guilty in exchange for a life sentence rather than the death penalty.

They were due to face trial in a military court at the maximum-security facility, but their cases have been bogged down in legal manoeuvring for years.

Karen Greenberg, the director of the Center on National Security at the Fordham University School of Law, said the deals were a significant development.

“It means a lot,” she told Al Jazeera. “It means that this trial, which has been put off for 12 years, will not happen. The issue has been resolved with this plea deal. It means the idea of bringing Guantanamo to closure is one step closer.”

Nearly 3,000 people were killed when members of the al-Qaeda group hijacked four domestic flights and flew them into the World Trade Center in New York, and the Pentagon building outside Washington. The fourth plane crashed into a field in Pennsylvania after passengers fought back against the hijackers.

The attack triggered what then-President George W Bush called the “war on terror”, leading to the US military invasions of Afghanistan and Iraq and years of US operations against armed hardline groups elsewhere in the Middle East.

The three men could appear in court as early as next week to formally enter their pleas.

Mohammed was regarded as one of al-Qaeda chief Osama bin Laden’s most trusted and intelligent lieutenants before he was captured in a covert operation in Pakistan in March 2003. He spent three years in secret CIA prisons before arriving in Guantanamo in 2006.

An engineer, who studied at a university in the US, Mohammed was subjected to waterboarding 183 times while in CIA custody before he was sent to Guantanamo, and was also targeted by other forms of torture and coercive questioning.

Bin Attash, a Saudi of Yemeni origin, allegedly trained two of the hijackers who carried out the September 11 attacks, and his US interrogators also said he confessed to buying the explosives and recruiting members of the team that killed 17 sailors in an attack on the USS Cole. He was captured with Mohammed in 2003 and was also held in a network of secret CIA prisons.

Hawsawi is suspected of managing the finances for the 9/11 attacks. He was arrested in Pakistan on March 1, 2003, and was also held in secret prisons before being transferred to Guantanamo in 2006.

The use of torture has proven one of the most formidable obstacles in US efforts to try the men in 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 in Cuba.

The military commissions at Guantanamo were established by former President Bush in 2001 to prosecute people accused of organising the September 11 and other attacks outside the bounds of US criminal law.