It has been nearly 23 years since the horrific 9/11 terrorist attacks; 21 years since the accused mastermind, Khalid Sheikh Mohammed, was captured in Pakistan by the CIA; 16 years since he was charged with war crimes, mass murder, and conspiracy; and five years since a military judge set a date for him and other Al Qaeda plotters to be tried at the US detention center at Guantanamo Bay.

But Mohammed and his confederates have yet to stand trial, and there seems little likelihood they ever will. Even if their cases eventually go forward, it is virtually guaranteed that they will never be sentenced to death for engineering the bloodiest terror attack in history. That isn’t because they don’t deserve to die. It is because so much of the information against them was acquired through torture.

Two weeks ago, US military prosecutors announced that Mohammed and two other Al Qaeda defendants, Walid bin Attash and Mustafa al-Hawsawi, had agreed to plead guilty to all charges and accept a sentence of life imprisonment. The plea deal enabled the government to avoid a lengthy and complicated death penalty trial, and to bring, in the prosecutors’ words, some “finality and justice” to a case that has spent decades going nowhere.

But the agreement triggered a backlash among families of the 9/11 victims, many of whom found it intolerable that Mohammed and his accomplices should be spared a potential death sentence. Bowing to pressure, Defense Secretary Lloyd Austin revoked the deal two days after it was unveiled. So now the defendants again face the prospect of capital punishment when their case goes to trial.

If it ever does.

In an address to Congress soon after Sept. 11, then-president George W. Bush called for a “war on terror” and vowed: “Whether we bring our enemies to justice, or bring justice to our enemies, justice will be done.”

Yet any chance of bringing Mohammed and his fellow conspirators to justice was wrecked early on by Bush’s decision to authorize the CIA to use “enhanced interrogation techniques” — a euphemism for torture — to break the terrorists’ resistance. According to the government, those techniques, especially the waterboarding to which Mohammed was repeatedly subjected, yielded lifesaving information. They “helped break up plots to attack American military and diplomatic facilities abroad, Heathrow Airport and Canary Wharf in London, and multiple targets in the United States,” Bush later recounted in “Decision Points,” his 2010 memoir. “Without the CIA program, there would have been another attack on the United States.”

To be fair, the nation was reeling from the horror of 9/11. Nearly 3,000 Americans had been killed and Bush was desperate to prevent another bloodbath. Indeed, evidence later emerged of plans to crash a hijacked airliner into a Los Angeles skyscraper in a second wave of attacks. It’s not hard to understand why US officials would decide that, with the stakes so grave, their highest obligation was to extract information from the Al Qaeda detainees, even if that meant using torture.

But if their decision was understandable, it was nevertheless wrong.

It was wrong because torture is illegal. The international Convention Against Torture, which the United States ratified in 1994, prohibits the torture of anyone for any reason by any government at any time. It specifies that there are “no exceptional circumstances whatsoever” under which torture can be justified. The ban on torture — which is explicitly incorporated into US law — is absolute.

It was wrong because torture is unreliable. To make the pain stop, many people will say anything, accuse anyone, admit to any offense. Sometimes torture generates lifesaving information. But at other times it results in false leads and red herrings.

It was wrong because, even with good intentions, a policy of torturing detainees will inevitably brutalize the innocent. Sure enough, when the Senate Select Committee on Intelligence compiled an exhaustive report on the CIA’s enhanced interrogation program, it found that more than two dozen tortured detainees had been wrongfully held. One of the abused was a mentally disabled man being used as “leverage.” The CIA even tortured two of its own informants.

And now we know that it was wrong for another reason: It has made it impossible to successfully prosecute, convict, and execute a monster like Mohammed, who by his own admission organized the 9/11 slaughter “from A to Z.” Information obtained through torture will never be admitted as evidence against the Guantanamo defendants. Without that evidence it is all but certain that no prosecution will succeed.

It was barbaric to torture Khalid Sheikh Mohammed. It was also an egregious blunder, one that may keep him alive until he dies of old age.