Khalid Sheikh Mohammed, the man said to be the main mastermind of the attacks on September 11, 2001, is expected in court on Tuesday.
The pre-trial hearing will take place on Guantanamo Bay, the Cuban island detention centre where Khalid Sheikh Mohammed has been held since his capture in 2003.
US authorities say Khalid has made at least 31 confessions and now faces the death penalty. He is accused of 2,973 individual counts of murder.
Human rights lawyer Clive Stafford Smith told Euronews the reason why the US legal system has taken so long to set up a trial is because Americans were "unwilling to trust our legal system, which we've had for over 200 years and we still can't get right".
"So the military just created a whole new system out of whole cloth, back in April 2003. But it's so full of huge legal mistakes that they just can't get their act in gear," he added.
Asked about how to ensure Khalid Sheikh Mohammed has a fair trial, after suspicions that he was subjected to torture in Guantanamo, Smith replied that he had undergone waterboarding, a technique the US government calls "enhanced interrogation".
"It's worth noting that in World War Two, the Gestapo used waterboarding. [...] We copied that. We didn't copy what the Inquisition called it in the Middle Ages, which was water torture. So here we are torturing people and pretending it's not torture and then thinking that we can give them a fair trial. It's just disgusting. We should have never got into that," Smith said.
Clive Stafford Smith, who has represented many people in Guantanamo, believes the detention centre is "a black stain" in the US democratic system.
"What we did is create an island prison where we deny everyone the rule of law. I was one of the three lawyers who brought Russell v. Bush, the very first case that opened it up to lawyers. And it's still a dreadful place," the human rights lawyer revealed.
Thirty-nine people are in Guantanamo Bay, and the US government is spending $12 million (€10,1 million) per prisoner per year.
"All it does for the United States is create a very bad reputation and make us look like hypocrites. So I do hope that it's closed down fairly soon, but I'm sceptical because the Republicans love to make it a political football. I think we may have Guantanamo for a few years to come," Smith told Euronews.
Watch the full interview in the video player above.