Davontae Sanford was 14 years old when he confessed to murdering four people in a drug house on Detroit’s East Side. Left alone with detectives in a late-night interrogation, Sanford says he broke down after being told he could go home if he gave them “something.” On the advice of a lawyer whose license was later suspended for misconduct, Sanford pleaded guilty in the middle of his March 2008 trial and received a sentence of 39 to 92 years in prison.

Sixteen days after Sanford was sentenced, a hit man named Vincent Smothers told the police he had carried out 12 contract killings, including the four Sanford had pleaded guilty to committing. Smothers explained that he’d worked with an accomplice, Ernest Davis, and he provided a wealth of corroborating details to back up his account. Smothers told police where they could find one of the weapons used in the murders; the gun was recovered and ballistics matched it to the crime scene. He also told the police he had used a different gun in several of the other murders, which ballistics tests confirmed. Once Smothers’ confession was corroborated, it was clear Sanford was innocent. Smothers made this point explicitly in an 2015 affidavit, emphasizing that Sanford hadn’t been involved in the crimes “in any way.”

But Smothers and Davis were never charged. Neither was Leroy Payne, the man Smothers alleged had paid him to commit the murders. (Through his attorney, Payne has denied any involvement.) Instead, Smothers pleaded guilty to the other eight killings. Davis, who was never prosecuted, was convicted of an unrelated felony in 2013 and could be released from prison as early as July. Payne, who remains a free man, left Detroit in 2016. His whereabouts are unknown.

Davontae Sanford, meanwhile, remained behind bars, locked up for crimes he very clearly didn’t commit.

Police failed to turn over all the relevant information in Smothers’ confession to Sanford’s legal team, as the law required them to do. When that information was leaked in 2009, Sanford’s attorneys sought to reverse his conviction on the basis of actual innocence. Wayne County Prosecutor Kym Worthy fought back, opposing the motion all the way to the Michigan Supreme Court. In 2014, the court sided with Worthy, ruling that actual innocence was not a valid reason to withdraw a guilty plea. Sanford would remain in prison for another two years.

 In an adversarial legal system, it’s natural to presume that prosecutors and defense attorneys are driven by the same goal: to win. They aren’t. In Berger v. United States, decided in 1935, the Supreme Court famously declared that the prosecution’s ultimate goal “is not that it shall win a case, but that justice shall be done.” A prosecutor, the court wrote, “is in a peculiar and very definite sense the servant of the law, the twofold aim of which is that guilt shall not escape or innocence suffer.”

Embracing this “twofold aim” is at the core of a prosecutor’s work. The government brings cases it believes are supported by proof beyond a reasonable doubt. A victory at trial proves them right. But if new evidence is uncovered showing the conviction was error-ridden to the point of unreliability, the imperative that “justice shall be done” requires prosecutors to admit they were wrong. This responsibility exists even if a defendant may be guilty—if, for example, crucial evidence was obtained by illegal means. The moral imperative underpinning this precept, though, is brought into sharpest relief when it appears the defendant is actually innocent.

Many prosecutors accept this responsibility and, when proven wrong, ask the judge to dismiss a case or settle by way of a plea bargain. But too many do not. Indeed, there is a class of prosecutors that might fairly be called innocence deniers.

These prosecutors do not “do justice” as the Supreme Court defines it. Instead, they delay justice and in some cases actively work against it. When a prisoner is exonerated by a lower court, these prosecutors double and triple down, filing appeal after appeal. Or they indict and prosecute the exoneree all over again, sometimes under a wildly different theory at the expense of time and resources that should be used to pursue the crime’s actual perpetrator. They may also threaten endless legal challenges to wring “no contest” pleas from innocent prisoners in exchange for time-served sentences. The prisoners, desperate to be free, accept these Faustian bargains, which brand them convicts for life and allow prosecutors to proclaim their guilt and the state to deny them compensation. Some prosecutors are so committed to adhering to the original mistake that they fail to prosecute the actual perpetrators, even when there is evidence to convict them.