Alleged 9/11 plotter Khalid Sheikh Mohammed and four others held at the Guantanamo Bay prison camp will finally go on trial in 2021, almost two decades after the devastating Al-Qaeda attack, the New York Times reported Friday.

A military judge at the US Navy's Guantanamo, Cuba base set the date for the death-penalty trial for January 11, 2021, according to the newspaper.

The date was included in a scheduling order for pre-trial activities by the military judge, Colonel Shane Cohen, the Times said.

The five will be the first to go on trial in the military commissions established to handle the "War on Terror" detainees captured and sent to Guantanamo after September 11, 2001 attacks that left 2,976 people dead in New York, Pennsylvania and Washington.

Mohammed, Walid bin Attash, Ramzi Binalshibh, Ali Abd al-Aziz Ali, and Mustafa al-Hawsawi were accused of planning and participating in the plot hatched by Al-Qaeda leader Osama bin Laden to hijack four airliners and crash them into New York's World Trade Center and buildings in Washington.

Two of the planes struck the World Trade Center, another hit the Pentagon and a fourth crashed into a field in Pennsylvania after passengers, having learned of the other flights, fought the hijackers.

The five were formally charged in 2012 with conspiracy, attacking civilians, murder in violation of the law of war, aircraft hijacking and terrorism.

Mohammed, a Pakistan native thought to be about 54, is a key figure in the trial: he has been accused of being the mastermind of the 9/11 plot.

He was captured in Pakistan in 2003. Turned over to the US Central Intelligence Agency, he underwent severe torture, including repeated waterboarding, as US officials sought to learn more about the plot and Al-Qaeda.