'Why is this so hard?" That question, asked by Col James Pohl, the military judge heading the proceedings against the alleged masterminds of the September 11, 2001 attacks, will not be answered easily. But it must be addressed if Americans are to find closure, and if the case against Khalid Sheikh Mohammed and four others is ever to be seen as legitimate.
This military tribunal is Mohammed's second; the first, in 2008, ended after the US Supreme Court rejected the rules of evidence. When US President Barack Obama assumed office in 2009, he tried to move the case to a civilian court, but public and political pressure stopped him.
So why is it so hard to try alleged 9/11 plotters? Part of the reason is procedural. Evidence is likely circumstantial. There are also concerns that airing details in open court might compromise military sources and informants.
The other, darker, question is how the testimony was obtained. Every US administration for the last 10 years has tried hard to avoid the word "torture", preferring "enhanced interrogation" to explain how confessions were obtained. Yet the abuses documented in Guantanamo Bay are torture by any standard: not merely simulated drowning, or waterboarding (Mohammed has been subjected to this torture 183 times), but the use of dogs against naked detainees, beatings and sleep deprivation.
Morris Davis, a retired US colonel who was a chief prosecutor at Guantanamo, denounced the tribunal that started at the weekend - interrupted with outbursts of shouting and prayer - as a farce. "The reason the apologists want a second-rate military commission option," he told The Guardian, "is because of what we did to the detainees, not because of what the detainees did to us."
There is more at stake here than closure for the families of the victims of September 11th (as important as that is). The process itself must be seen as fair, not only to Americans, but in the eyes of the world. Mr Obama himself has recognised that Guantanamo has become a recruiting tool for Al Qaeda. It is also a glaring example of US hypocrisy - chastising other governments on human rights only to shirk them at a naval base in Cuba.
If this is how the US treats its detainees, what moral reason can there be for other governments not to do the same? And if justice is not possible for the lowest hanging fruit in Guantanamo, what about the others still in detention?
There are no easy answers to these questions. Justice related to terror suspects is indeed a dilemma for Mr Obama. Failing to address these challenges, however, will only deepen the distrust for the US that the last decade has nurtured.
