As America marks the 25th anniversary of the September 11 attacks, the man accused of masterminding the plot remains behind bars at Guantanamo Bay — without ever having faced trial.Khalid Sheikh Mohammed has spent two decades at the U.S. military detention center in Cuba, and despite a judge recently setting a June 5, 2028 trial date, some lawyers believe the case may never reach a verdict.At the heart of the extraordinary delay is Mohammed's treatment after his 2003 capture in Pakistan. He was held for more than three years in secret prisons and subjected to torture in CIA custody, including 183 instances of waterboarding, according to a U.S. Senate report.Khalid Sheikh Mohammed, the alleged Sept. 11 mastermind, is seen shortly after his capture during a raid in Pakistan, March 1, 2003 (AP2003)The consequences continue to complicate the government's case.In August, a military judge ruled that prosecutors could not use an alleged confession Mohammed made to the FBI in 2007, finding the statements were tainted by the "enhanced interrogation techniques" used against him.The government declined to appeal, in part because doing so risked delaying the case even further."It's all contaminated by politics and the lack of accountability on torture," said Joshua Dratel, an attorney who helped ensure Mohammed received legal representation.A woman looks at names on the South Pool at the 9/11 Memorial & Museum ahead of the 25th anniversary of the September 11, 2001 attacks (Reuters)Mohammed, accused of developing and directing the 9/11 plot as an al-Qaida leader, was transferred to Guantanamo Bay on Sept. 5, 2006.For families of the nearly 3,000 people killed on Sept. 11, 2001, the wait for a resolution has now lasted a quarter-century.Terry Strada, whose husband, Tom, was killed at the World Trade Center, said families still want to see Mohammed brought to justice."We very much want to see this come to an end at some point. We do want to see justice served. It's just as important as 25 years ago," said Strada, national chair of 9/11 Families United.Strada said she would rather see Mohammed remain imprisoned indefinitely at Guantanamo than support an agreement that removed the possibility of the death penalty.Terry Strada, shown here, whose husband, Tom, was killed at the World Trade Center, said families still want to see Mohammed brought to justice (Getty)A plea deal that would have spared Mohammed a possible execution in exchange for life imprisonment began unraveling shortly after it was announced in 2024 and collapsed for good last year.Strada said she fears that without a death sentence, a future administration could potentially seek to exchange Mohammed for Americans imprisoned overseas.The death penalty "fits the crime and it would prevent that from ever happening," she said.There was once a plan to put Mohammed on trial just blocks from where the World Trade Center stood.In 2009, then-Attorney General Eric Holder announced that Mohammed and four other men charged over the attacks would face a civilian trial in Manhattan.Then-President Barack Obama, who had pledged to close Guantanamo, said Mohammed would face "the most exacting demands of justice."In 2009, then-Attorney General Eric Holder announced that Mohammed and four other men charged over the attacks would face a civilian trial in Manhattan (Getty)But the proposal quickly encountered fierce opposition. Critics raised security concerns and warned that Mohammed could use proceedings as a platform for extremist views.Former New York City Mayor Rudy Giuliani called the plan unwise and accused the administration of showing "a lack of concern for the rights of the public."The civilian trial was ultimately abandoned, leaving the case to the military commission system.Dratel described the abandoned effort as "a charade in many respects" but said the military tribunal system had proved even less effective."Each time you reach an impasse, no one knows what to do," he said.David Raskin, the former federal prosecutor who would have led the government's New York case, argued this week that a civilian prosecution likely would have secured a conviction.Instead, he wrote in The Washington Post, the military commission became "a defense lawyer's dream," plagued by years of litigation over its legality and procedures.Twenty-five years after the attacks and more than two decades after Mohammed's capture, Raskin believes the wait may never end."I predict there will never be a completed military commission trial for Mohammed and the other Sept. 11 defendants," he said.