Accessible only by U.S. military transport, the Guantanamo Bay prison’s location has been a factor in slowing the pace of the trials. When lawyers travel to the island, they must hitch a ride on military planes and stay several days at a time. (Lucas Jackson /Reuters)

When the George W. Bush administration announced in September 2006 that 14 major terrorism suspects had arrived at Guantanamo Bay, Cuba, military lawyer Morris Davis heralded it as a sign of the government’s commitment to attaining justice.

For Davis, then chief military prosecutor at the top-security facility, the end of the suspects’ detention at secret CIA prisons overseas promised a credible legal reckoning in the wake of the Sept. 11, 2001, attacks.

“I want our grandchildren to look at Guantanamo the way we look back at Nuremberg,” Davis told the lawyers on his team, offering as a model the prosecution of Nazi officials that followed World War II. “We felt we had the ability to conduct these trials in a way that . . . the country would be proud of.”

Ten years later, none of those 14 “high value” detainees brought to Guantanamo Bay have been convicted or sentenced in the military commissions. Roughly half a dozen cases tried in other commission proceedings have resulted in convictions, but most have been thrown out on appeal.

A clutch of cases is moving so slowly in preliminary proceedings that the trial of five suspects accused of organizing the 9/11 attacks is expected to begin at the earliest in 2020, nearly 20 years after hijacked planes struck the World Trade Center and the Pentagon.

In the same period, hundreds of terrorism suspects have been convicted in federal courts, including members of al-Qaeda captured overseas. But Congress has barred the Obama administration from moving any Guantanamo detainees into the United States, which leaves offshore military commissions as the only legal process available to prosecute them. The administration had planned to prosecute the 9/11 defendants in federal court in New York, but after congressional and local opposition, their cases were returned to the military legal system in 2011.

The military commissions process has been plagued from the start by detours and scandals, including the legacy of the use of torture against detainees, an FBI attempt to penetrate a defense team and the unexplained censoring of court deliberations, believed to be the work of the CIA.

Despite President Obama’s effort to improve the commissions by giving inmates greater due process, legal experts and lawyers who have been involved in the trials say the system may be irreparably flawed.

Some lawyers say that even if the cases can be concluded, the process is now seen as so tainted that those verdicts may be publicly dismissed.

“The fact that we are here in 2016, probably further from trial than we were in 2011, tells you that this is an experiment that failed,” said Richard Kammen, a civilian defense lawyer for one of the high-value detainees.

Lt. Col. Valerie Henderson, a spokeswoman for the Pentagon, said military judges and lawyers have been working to put the necessary pieces in place for the eventual trials to begin. “The Department of Defense is committed to fairness and transparency in the military commissions proceedings,” she said.

President George W. Bush announces the transfer of “high value” terrorism suspects from secret CIA sites to the Guantanamo prison on Sept. 6, 2006. (Charles Dharpak/AP)

In 2009, Obama laid out his plan for “cleaning up something that is, quite simply, a mess,” referring to the prison and trial process set up under President Bush, who brought hundreds of detainees to Guantanamo in the months after the 9/11 attacks.

“As president, I refuse to allow this problem to fester,” Obama vowed. “I refuse to pass it on to somebody else.”

When Brig. Gen. Mark Martins became the commissions’ lead prosecutor in 2011, he asked the public for patience as he sought to demonstrate that the commissions could provide authentic justice despite the legacy of torture, the complexity of the cases and the challenge of handling a large volume of classified materials. Martins declined to comment for this article.

Perched in a remote corner of Cuba and accessible only by U.S. military transport, the Guantanamo prison’s very location has been an important factor in slowing the pace of the trials.

When lawyers travel to the island for periodic proceedings or client meetings, they must hitch a ride on military planes and stay for several days at a time. When they speak to the detainees, the materials they bring in and out of meetings are closely screened. Despite Pentagon denials, defense lawyers also suspect that communications with their clients continue to be monitored.

Defense lawyers describe a “down the rabbit hole” process in which they lack normal access to evidence, including what their clients said and did during their years-long detentions at extrajudicial prisons overseas, as well as evidence seized during counterterrorism raids.

Legal experts also say the untested nature of the commission system, which unlike civilian courts is operating without the benefit of relevant legal precedents to guide it, has slowed the process.

“We’re 13 years down the road, and you’re just now getting the defendants’ statements to the judge,” said David Nevin, a civilian defense lawyer for Khalid Sheik Mohammed, described as the 9/11 mastermind. “That’s pretty amazing if you’ve been around the criminal justice system.”

Earlier this year, defense lawyers learned that a judge had secretly allowed the prosecution to destroy evidence related to a CIA prison, reversing a previous judge’s order without notifying them.

It remains unclear what material from a 2014 Senate Intelligence Committee report on the CIA interrogation program will be permitted in the eventual trials and sentencing proceedings. That investigation showed that some detainees at the CIA’s secret “black sites” were subjected to extreme measures, including “near drownings” and “rectal rehydration.”

Some lawyers say the system has fundamentally different goals than the civilian courts.

“It is not a justice system in the way we in the U.S. think about it,” said James Connell, an attorney for Ali Abdul Aziz Ali, one of the 9/11 defendants. “It is instead a hybrid specialized system that was set up with the purpose of concealing evidence of torture.”

The White House declined to comment on the commissions, which many senior officials also view as flawed.

Defense lawyers said they don’t know what considerations will be made in court for the mistreatment of detainees. Abd al-Rahim al-Nashiri, accused in the 2000 attack on a U.S. ship off Yemen, was tortured while in CIA custody and has not received meaningful treatment for the significant psychological and physical effects he has suffered, said Kammen, one of his defense lawyers.

“Nashiri is profoundly damaged by what the CIA did to him,” he said.

It’s also possible that the trials will eventually be dropped, if political leaders decide that they are unfeasible or if moving forward would force the government to disclose information seen as too damaging.

Many legal experts say transfer to federal courts is the only solution. Such courts have proved that they can handle complex terrorism cases, like that of Boston Marathon bomber Dzhokhar Tsarnaev, who was sentenced to death two years after the crime.

“We’ve lost sight of the basic question, which is: Why are we trying these people?” said Stephen Vladeck, a law professor at the University of Texas at Austin and a former Guantanamo defense lawyer.

“If the answer is to obtain some measure of justice for their heinous acts, the question the next president has to ask is whether it’s more likely . . . in a federal system or a Guantanamo military commission,” he said. “I think that question answers itself.”

Julie Tate contributed to this report.