If it wasn’t for Mike Bloomberg, the alleged perpetrators of the worst terrorist attack in American history would likely have been convicted of mass murder by now.

According to all the evidence available both at the time and in the nine years since Bloomberg’s intervention, a federal court almost certainly would have convicted the five co-defendants. A judge would have had to reckon with the torture the CIA inflicted on them, barring the prosecution from using tainted evidence—and showing, for the record, how torture jeopardized the case. Most importantly, there would have been closure, provided in open court and displaying the inheritance of centuries of jurisprudence, for the atrocity of 9/11 and the brutality America chose when confronting it.

“ I remember the hopes I had that there would be a federal trial, and I remember when Bloomberg and others came together and said it wasn’t going to happen. ” — Terry Rockefeller

All that was why Eric Holder, then the attorney general, announced in November 2009 that the Justice Department would bring criminal charges against Khalid Shaikh Mohammed, Ammar al-Baluchi, Ramzi Binalshibh, Walid bin Attash, and Mustafa Ahmed al-Hawsawi, who—then as now—were detained at Guantanamo Bay. The venue for the trial was to be the federal courthouse in Manhattan, a short walk from the former site of the World Trade Center.

It was an even shorter walk to City Hall, where Michael Bloomberg presided as mayor. Bloomberg at first backed trying the 9/11 conspirators in the city. But the NYPD and the big real estate developers central to Bloomberg’s vision of New York as a “luxury brand” viewed the trial as a national-security version of a Not-In-My-Backyard concern—all as a broader backlash to Barack Obama’s handling of the war on terror was brewing. By January 2010, Bloomberg reversed himself, and his opposition doomed the trial.

“I remember the hopes I had that there would be a federal trial, and I remember when Bloomberg and others came together and said it wasn’t going to happen,” said Terry Rockefeller, whose sister died in the World Trade Center and who apportions blame for the trial’s collapse on Holder as well. “It’s just been the most frustrating reflection on what we’ve done as a nation that this many years later we can’t have a trial.”

The episode is less remembered than Bloomberg’s defense of racist policing, his accommodation of police Islamophobia, his history of misogyny and his affinity for foreign authoritarians, all of which Bloomberg shares with the occupant of the White House he seeks to dislodge. But it had a devastating effect on the Obama administration’s ambitions for emptying the wartime prison in Cuba and proving the merits of civilian courts over military tribunals for what Holder had called the trial of the century. Eighteen years after 9/11, justice for the attack remains locked away in Guantanamo.

“It’s hard to overestimate the damage that Bloomberg’s opposition to holding the 9/11 trials in New York federal courts caused,” recalled Karen Greenberg, the director of the Center on National Security at Fordham University. “The inability to have closure on the 9/11 attacks, which this country is still owed; the lack of trust in the federal criminal justice system; and the perpetuation of Gitmo—it is an incalculable misstep, and it pulled the rug out from under Obama and Holder’s conviction that the 9/11 trials needed to be held in federal court on federal soil, just as [international terrorism cases] had always been prior to 9/11.”

Joseph Marguiles, attorney for Abu Zubaydah, another Guantanamo detainee tortured by the CIA, said Bloomberg’s rejection of the trial showed the same “fear-mongering and bone-headedness” as his embrace of stop-and-frisk.

“It’s all of a piece: a mindless, reflexive cowardice,” Marguiles said.

Representatives for Bloomberg’s campaign did not respond to messages seeking comment. Holder, through a spokesperson, declined comment. So did Holder’s national security adviser at the time, Amy Jeffress.

Barack Obama came into office pledging to close Guantanamo Bay, but quickly alienated civil libertarians by his parsimonious definitions of what closure meant. Rather than forsake military detention away from the battlefields of Iraq and Afghanistan, Obama sought to replicate it at an Illinois prison that critics derided as “Gitmo North.” By the spring of his first year in office, he proclaimed himself open to indefinite military detention for the “toughest” cases, even as he pledged he would seek civilian prosecutions for terrorist suspects “whenever feasible.”

The centerpiece for that feasibility was the 9/11 trial. For years, the 9/11 co-conspirators had languished in unofficial CIA prisons known as black sites where they faced torture so extreme that one of them, Hawsawi, experienced a rectal prolapse. Holder called prosecuting them in federal court the “defining event” of his tenure atop the Justice Department. He had support from important New York politicians. “New York is not afraid of terrorists,” boasted Rep. Jerrold Nadler, a Democrat representing Manhattan.

Bloomberg, at first, joined the chorus. “It is fitting that 9/11 suspects face justice near the World Trade Center site where so many New Yorkers were murdered,” he said the day of Holder’s announcement. Doing so was entirely feasible, he noted, as proven by the federal trial for the 1993 World Trade Center bombing. Bloomberg said he had spoken to Holder and pledged city support “in any way necessary.” He expressed confidence in the NYPD’s “experience dealing with high-profile terrorism suspects and any logistical issues that may come up during the trials.”

But he quickly developed other ideas.

By the time the Justice Department announced its intended 9/11 trial, a backlash to Obama was coalescing around the country. One of its focal points was Obama’s emphasis on using the criminal justice system for terrorism cases, which the right interpreted as a five-alarm fire. Mitch McConnell, the Senate GOP leader, led an early charge warning “how dangerous closing Guantanamo could be.” Then, weeks after the Justice Department announcement, FBI agents read a Miranda warning to a Nigerian jihadist named Omar Farouk Abdulmutallab who tried and failed to blow up a civilian airliner as it descended into Detroit. Abdulmutallab extensively cooperated with investigators, but to the right, it crystallized a danger Obama allegedly posed. Rudy Giuliani wailed, “Why in God’s name would you stop questioning a terrorist?”

The 9/11 trial suddenly had a new, hysterical context. A rally at Foley Square in December, featuring relatives of 9/11 victims, denounced the attorney general. It was organized by a group led by Islamophobic 9/11 widow Debra Burlingame, future Rep. Liz Cheney and neoconservative pundit Bill Kristol, called Keep America Safe—explicitly meaning safe from terrorism and, tacitly, from Obama. Accordingly, the crowd around or passing by Foley Square yelled “traitor” and “lynch Holder!”

Then there were more parochial concerns. The NYPD began worrying aloud that the trial would be a logistical snarl, and ratcheted up their estimates of its cost. Commissioner Ray Kelly briefed community officials with intimidating projections about blanketing downtown Manhattan with police checkpoints and intrusive searches. The police weren’t the only influential constituency that blanched. The New York Times reported that Bloomberg got “an earful” of opposition to the trial when he attended an annual gathering of the Real Estate Board of New York; its president warned “it would destroy the economy in Lower Manhattan.” Jane Mayer of The New Yorker noted that “companies with downtown real-estate interests had been lobbying to stop the trial.” The chairwoman of the downtown-Manhattan community board wrote an op-ed opposing having the trial “in the midst of a dense residential and office neighborhood.”

By early January, weeks after supporting the trial, Bloomberg reneged. In a letter to the White House, Bloomberg asserted a security threat to the trial that he felt no political pressure to explain. Now the trial would cost the city over $200 million annually, largely due to reallocating police officers, who would accrue “significant overtime.” Bloomberg, backed by Kelly, expected federal reimbursement—something he insisted would not be a “blank check.” Bloomberg was backed by his home-state senator, now-Democratic Senate leader Chuck Schumer, who insisted that “not a nickel of these costs should be borne by New York taxpayers.”

It happened that there was a test case undercutting Bloomberg’s argument in real time. In June 2009, federal prosecutors in New York indicted a different Gitmo detainee, someone whom the CIA also tortured in the black sites. The trial of Ahmed Khalfan Ghailani wasn’t on the scale of the 9/11 trial—he was indicted for his role in the 1998 bombings of U.S. embassies in Kenya and Tanzania—but it featured no security disruption from terrorists, no abnormal police presence, and no economic disaster. Its judge, Lewis Kaplan, refused the government one of its desired witnesses, someone whom Ghailani named during his black-site interrogations. A jury acquitted Ghailani of all but one count of conspiracy, but it was enough to sentence him to life in prison in 2011, a sentence that has survived Ghailani’s appeals. His trial took a month.

But by then, the 9/11 trial had long been a lost cause. At a press conference on a Wednesday in late January, fueled by a nonbinding community-board vote against the trial, Bloomberg said that his “hope is that the attorney general and the president decide to change their mind” and hold the trial elsewhere. Two days later, Justice Department officials conceded to Times reporters that it was now “obvious” the trial couldn’t happen in New York.

“If these trials were going to take place anywhere, they’d take place in New York, and the mayor of the largest city in the country said they can’t handle it. Well, if you can’t do it there, you can’t do it anywhere,” Marguiles said. “It was just nonsense. Of course they could have done it. These cases would have been resolved 10 years ago.”

That November, before the Justice Department could salvage the prosecutions and indict Mohammed and his co-conspirators elsewhere, the Republicans won control of Congress. Once in office, the new GOP majority spearheaded legislation barring the Pentagon from spending money to move Guantanamo detainees onto mainland American soil, effectively killing any federal criminal indictment of anyone held in the wartime prison, a prohibition that continues to this day. Conceding defeat, the Obama administration in 2012 re-indicted the five co-conspirators in a military commission held at Guantanamo.

“ This country continues to live inside the post-9/11 moment in a way that didn’t need to happen. ” — Karen Greenberg

The death of the 9/11 trial didn’t stop Obama from prosecuting terror suspects, something Donald Trump’s Justice Department has pursued as well. “It just became impossible to resolve the stain of 9/11 and the reality of Guantanamo,” Marguiles observed. “Everything about the show trial taking place down at Gitmo is inferior.”

Indeed, the 9/11 military tribunal has lasted almost eight years without proceeding to trial. It’s been beset by a baroque series of setbacks, including accusations of government spying on the defense attorneys. Its new judge has set a trial date for 2021, some 20 years after 9/11, but that target is, as ever, in doubt. This week, one of Binalshibh’s attorneys, James Harrington, sought to remove himself from the case on health grounds. To keep the trial date alive, the prosecution took the extraordinary step of motioning to keep Harrington involved.

Like many attorneys—including Holder—Greenberg and Marguiles believe the abundance of evidence about the 9/11 plot obtained outside of torture is sufficient to secure a federal conviction for the accused co-conspirators. As well, Marguiles said the 9/11 trial would have provided a way to “reckon with the legacy of torture.”

Without a trial, New Yorkers and Americans generally lack the “closure and a narrative” that court cases provide, Greenberg said. “This country continues to live inside the post-9/11 moment,” she said, “in a way that didn’t need to happen.”

No one continues to live in that moment more than the thousands of people like Rockefeller, who lost their loved ones on 9/11. “It was a crushing failure of will to actually do the right thing, to try the [accused conspirators] in a federal court,” said Rockefeller, who is affiliated with Sept. 11 Families for Peaceful Tomorrows. “That would have been to say that our pride in our rule of law, and our belief in our legal system, is what makes us different from terrorists.”