SEVENTY CONVICTED murderers had their guilty verdicts thrown out last year, the highest number since researchers at the University of Michigan Law School began tracking exonerations in 1989. African Americans were disproportionately represented among them, which is unsurprising given that over the past 30 years blacks have been seven times more likely to be wrongfully convicted of homicide than whites.

Still, it was remarkable when Corey Atchison, a 48-year-old black man, last week had his homicide conviction thrown out by a judge in Tulsa, Okla., three years after his younger brother was cleared, also of a first-degree murder conviction, by the same judge — in a completely unrelated case. The brothers’ wrongful convictions represent the sort of serial failure of justice that wrecks lives and shreds confidence in the system.

In the case of Mr. Atchison and his brother, Malcolm Scott, the system produced what Oklahoma District Judge Sharon Holmes concluded were fundamental miscarriages of justice that resulted in the two men serving a combined total of close to 50 years behind bars — nearly 30 for Mr. Atchison; 21 for Mr. Scott. In 2017, Mr. Scott, in a federal lawsuit seeking damages for his wrongful conviction from the city of Tulsa and a pair of former detectives, declared he wanted compensation for “unfathomable wrongs” that robbed him of his liberty as a 17-year-old.

Imagine you're a public defender in a criminal-justice system that penalizes people who want their day in court. What do you do? (Danielle Kunitz, Kate Woodsome/The Washington Post)

In both cases, those wrongs appear to have involved police investigators who coerced witnesses into giving false testimony. Without those witnesses, the judge said of Mr. Atchison’s case, it’s unlikely a jury would have found him guilty in the murder of James Lane, who was shot to death in a robbery in 1990. Other witnesses whose accounts might have persuaded a jury to find Mr. Atchison not guilty were not called to testify in his 1991 trial.

The reversal of Mr. Scott’s murder conviction, and that of a co-defendant, De’Marchoe Carpenter, involved the drive-by shooting death of a 19-year-old woman, Karen Summers. Both men, teenagers when they were convicted, were sentenced to life in prison. It was only with the help of a private investigator and the Oklahoma Innocence Project, a clinic at the Oklahoma City University School of Law, that another man, against whom charges in the same murder were dropped, ultimately confessed that he fired the fatal shots. (His confession came just before he was executed, in 2014, for another murder.) Other witnesses recanted the testimony they gave at trial.

The private investigator, Eric Cullen, began looking into Mr. Scott’s and Mr. Carpenter’s convictions in 2006 and quickly concluded that they were innocent; it took a decade for a court to reach the same conclusion. As it happens, Mr. Cullen was also instrumental in unearthing evidence and testimony that led to Mr. Atchison’s exoneration.

The fact of Mr. Cullen’s involvement, more than any innate self-corrective mechanism in the judicial system, was the critical factor in these cases. Had he not come along, and had he been less persistent, the men would likely still be incarcerated — and would have remained so until their deaths. Which raises the question: How many other wrongly convicted men and women are wasting away behind bars, victims of overzealous or corrupt police and prosecutors and a judicial system too often ill-equipped to render its most basic obligation: justice?

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