Fifty years ago, Americans set out on a polarizing mission: to find a just and fair way to punish the worst-of-the-worst crimes by execution.

In some ways, this was a surprising choice. In 1972, a narrow majority of the US supreme court had scrapped the country’s entire death penalty system, calling it “morally unacceptable”, “racially discriminatory” and “arbitrary”. It seemed possible that Americans might join our peers in Europe and Latin America, many of whom had ended executions for good.

But then Americans, as we often do, went our own way. In the summer of 1976, the supreme court issued another landmark decision, Gregg v Georgia, that brought the death penalty back with a set of attempted fixes intended to make it less arbitrary, including guidance for jurors and automatic appeals.

On the 50th anniversary of Gregg v Georgia, the Marshall Project analyzed more than 9,000 death sentences handed down across the nation since states brought the punishment back. The analysis also coincides with the release of The Last 12 Weeks, the Marshall Project’s new podcast with Serial Productions and the New York Times. The podcast features a case that has dragged on for more than 30 years, and the data suggests this is typical: people on death row and the families of their victims often have to wait decades for a resolution to their cases.

Most of the time, the outcome is not an execution.

If one goal of the death penalty is to deter crime, it’s hard to imagine anyone being deterred by a very low chance of being executed decades in the future. Last week, the Ohio governor Mike DeWine called for his state to abolish the death penalty, due to its failure as a deterrent and the emotional cost to victims’ families.

“Our system is an epic fail,” said Frank Baumgartner, the University of North Carolina at Chapel Hill professor who spent years gathering the data with his students. “Every flaw they sought to rectify has been a failure, and now there are new problems that didn’t used to exist.”

Black people are still overrepresented on state death rows. And whether someone gets the death penalty still depends more on where they commit a crime than on the crime itself. But the new data also reveals how rarely a death sentence ends as lawmakers intended: fewer than one out of every five people sent to death row has been executed.

Supporters and opponents of capital punishment can debate who is to blame for this dysfunction, but the new data gives us a window into why the death penalty remains so broken.

States passed new laws and started issuing new death sentences in 1972, inviting the supreme court to approve these efforts a few years later. Soon after, a network of highly skilled defense lawyers emerged – often with federal funding – to specialize in death row appeals. (The Last 12 Weeks features several such lawyers.)

These lawyers often opposed the death penalty as racist and immoral. They dug into trial transcripts and sent out investigators who found all kinds of problems, from prosecutors making racist statements and kicking Black people off juries to defense lawyers literally falling asleep at trial. Eventually, defense lawyers convinced the supreme court to nix the death penalty for crimes committed before the defendant turned 18 and for people with intellectual disabilities.

All of these developments – the failures at trial and the defenses’ successes at finding them – help explain why more than a third of death sentences handed down over the last 50 years have been thrown out by the courts. When that happens, prosecutors can seek a new death sentence, and sometimes they do so multiple times. Curtis Flowers, whose case was made famous by the podcast In the Dark, faced the death penalty in Mississippi courts six times before the charges against him were finally dropped.

In other cases, prosecutors have agreed to let the defendant plead guilty in exchange for a life sentence, or jurors refused to give the death penalty again. “It’s such an inefficient system, as you’re wasting huge amounts of money on capital trials that end up in reversals 20 years later,” Baumgartner said. These trials regularly hit the million-dollar mark to pay for all the lawyers, investigators and expert witnesses involved.

The 1990s saw the emergence of DNA testing and legal efforts to overturn wrongful convictions, like the Innocence Project. It became more common for judges to free people from death row – one out of 50 cases since 1972 – due to evidence of their innocence.

But it wasn’t always a court that stepped in to stop an execution: in more than 400 cases, a governor or president has commuted someone’s death sentence. The reasons vary. Sometimes it’s because a state abolishes the death penalty, as 23 have done. Other times, a leader wants to stop a successor from executing people; Joe Biden freed 37 men from federal death row before leaving office. (He did not free three men convicted of mass shootings whose commutations would have been especially controversial: Dylann Roof, Dzhokhar Tsarnaev and Robert Bowers.)

Another big reason why people are not executed can be boiled down to politics. Support for the death penalty in polls has declined to about 50%. Amid pressure from activists and the public, pharmaceutical companies began refusing to sell their products for lethal injections. Governors like Ron DeSantis of Florida and Greg Abbott of Texas made executions a priority, and their states found new suppliers or alternate methods like firing squads. But others gave up.

Meanwhile, some governors oppose the death penalty on paper, but risk political blowback if they go too far. Gavin Newsom of California and Josh Shapiro of Pennsylvania both halted executions in their states, but neither has commuted any sentences. The result is that more than 700 people remain on death row in those states – a de facto life sentence that costs far more taxpayer money, given the ongoing appeals.

Of the more than 9,000 death sentences over the last half-century, 8% of cases have ended with the condemned person dying by causes other than execution. Some of those ended in suicide. At least one person was killed by another prisoner.

Put together complex legal processes and political ambivalence, and the result is a system that takes a very long time to reach unpredictable outcomes.

The average person executed last year waited on death row for almost 27 years. Three decades ago, the average wait was only 12 years. The irony is that lawmakers have spent a lot of that time trying to limit appeals and quicken executions. They have evidently failed, while also increasing the risk of executing innocent people, by restricting what kinds of evidence they can bring to court.

There are now more than 2,000 people on death rows across the country. More than a quarter of them have been there for more than 30 years. “They’re not leaving, so they’re just going to go into geriatric care,” said Baumgartner.

The punishment’s future is anything but clear. Jurors are sending fewer people to death row. At the same time, Donald Trump is pushing for a revival and talking about bringing back firing squads. But there is little indication that any of the problems that have bedeviled the punishment for the last half century – the racial disparities, the arbitrary outcomes, the endless waiting, the risk of executing the innocent – have been fixed, or whether they can be.

This article was published in partnership with the Marshall Project, a non-profit news organization covering the US criminal justice system