A federal judge's decision today -- excluding key testimony from the first civilian trial of a Guantanamo detainee -- is the latest, and potentially most significant, in a series of government losses in Gitmo-related cases that relied on evidence gained during coercive interrogations.

Ahmed Khalfan Ghailani, accused of participating in the 1998 al-Qaida bombings of U.S. embassies in Kenya and Tanzania, had been set to go on trial Wednesday in Manhattan. Judge Lewis Kaplan's ruling blocks prosecutors from calling a witness, Hussein Abebe, who was expected to testify that he had sold Ghailani the explosives used in one of the attacks. Prosecutor Michael Farbiarz had called Abebe a "giant witness for the government."

Judge Kaplan postponed the trial until Oct. 12 while the government considers whether to appeal the ruling.

The judge concluded that the information from Abebe was the "close and direct result" of coercive interrogations that Ghailani had faced in CIA custody. Three days of pretrial testimony by FBI and CIA officials failed to persuade Judge Kaplan that the government would have gotten the same information from Abebe without using Ghailani's interrogation statements, which prosecutors conceded had been coerced. Relying on coerced evidence would be unconstitutional, the judge explained. (Read the judge's order.)

As the first civilian prosecution of a Guantanamo prisoner, the Ghailani case is widely viewed as a bellwether for the Obama administration, which insists that ordinary federal courts can effectively try suspected terrorists. But, as we detailed in a recent story published in partnership with the National Law Journal, coercion-tainted evidence has already played a part in the government's losing a number of federal lawsuits filed by detainees seeking release -- and could foreclose future criminal prosecutions in military or civilian court.

The government has lost at least eight detention challenges in which inmates claimed incriminating statements had been made up in fear of aggressive questioners. Judges condemned interrogation methods ranging from verbal threats to physical abuse they called torture. (See our chart of Gitmo detainee suits.)

Ghailani has claimed he was tortured during several years in CIA custody at secret prisons overseas, before his transfer to Guantanamo in 2006.

In a side note that seemed to underscore the importance of the evidence he was excluding, Judge Kaplan stressed that, even if the government goes on to lose the case, Ghailani is unlikely to go free. He wrote in a brief order that the defendant's "status as an ‘enemy combatant' probably would permit his detention as something akin to a prisoner of war until hostilities between the United States and al-Qaida and the Taliban end."

The statement echoed assurances Obama officials have given in congressional testimony that acquittals in criminal trials would not necessarily result in the release of Guantanamo detainees. The law of war, the administration has argued, justifies prolonged detention regardless of trials for many of the 174 remaining captives. Officials have already said that at least 48 of the prisoners will be held indefinitely because they're too dangerous to release but can't be prosecuted successfully in military or civilian court.

Judge Kaplan said that he'd written a detailed opinion explaining his decision, but that it needed to be declassified before the public could see it.

The events unfolded on the 26th floor of the federal courthouse in lower Manhattan, in one of the building's largest courtrooms. Reporters appeared to outnumber other onlookers. Indoors extra security had been put in place, including a second metal detector and X-ray machine just outside the courtroom and the requirement that attendees be escorted from the lobby by a U.S. marshal.

But outside life appeared to go on as usual. The surrounding streets remained open, and passers-by took little notice of the few additional uniformed officers stationed on the sidewalks or of the media presence. Reporters and television cameras crowded into a makeshift pen of metal police barricades, awaiting a promised statement from Ghailani's attorney, but the cluster was modest for a courthouse where headline-making cases are routine.

Flanked by a half-dozen colleagues, defense lawyer Peter Quijano delivered a few short sentences. "This case will be tried upon lawful evidence – not tortured, not coerced," he said. "It is the Constitution that won a great victory today." The group turned and re-entered the courthouse, leaving many questions unanswered.