The Innocence Project released a report Tuesday alleging that prosecutors across the country are almost never punished when they withhold evidence or commit other forms of misconduct that land innocent people in prison.

The Innocence Project, a nonprofit legal group that represents people seeking exonerations, examined records in Arizona, California, Texas, New York and Pennsylvania, and interviewed a wide assortment of defense lawyers, prosecutors and legal experts.

In each state, researchers examined court rulings from 2004 through 2008 in which judges found that prosecutors had committed violations such as mischaracterizing evidence or suborning perjury. All told, the researchers discovered 660 findings of prosecutorial error or misconduct. In the overwhelming majority of cases, 527, judges upheld the convictions, finding that the prosecutorial lapse did not impact the fairness of the defendant’s original trial. In 133 cases, convictions were thrown out.

Only one prosecutor was disciplined by any oversight authorities, the report asserts.

The report was issued on the anniversary of a controversial Supreme Court ruling for those trying to achieve justice in the wake of wrongful convictions. In a 5–4 decision in the case known as Connick v. Thompson, the court tossed out a $14-million dollar award by a Louisiana jury to John Thompson, a New Orleans man who served 18 years in prison for a murder and robbery he did not commit.

The majority ruled that while the trial prosecutors had withheld critical evidence of Thompson’s likely innocence – blood samples from the crime scene – the Orleans Parish District Attorney’s office could not be found civilly liable for what the justices essentially determined was the mistake of a handful of employees. The decision hinged on a critical finding: that the District Attorney’s office, and the legal profession in general, provides sufficient training and oversight for all prosecutors.

The Innocence Project study echoes a 2013 ProPublica examination focused on New York City prosecutors. In 2013, ProPublica used a similar methodology to analyze more than a decade’s worth of state and federal court rulings. We found more than two dozen instances in which judges explicitly concluded that city prosecutors had committed harmful misconduct.

Several of the wrongfully convicted people in these cases successfully sued New York City. In recent years, New York City and state have doled out tens of million dollars in settlements stemming from such lawsuits. Former Brooklyn District Attorney Charles Hynes was voted out of office, in part because of wrongful convictions gained through misconduct on the part of his prosecutors or police detectives working with them.

But only one New York City prosecutor, ProPublica’s analysis found, was formally disciplined: Claude Stuart, a former low-level Queens Assistant District Attorney, lost his license. He was involved in three separate conviction reversals.

Just as we found in New York, the Innocence Project’s report found that appellate judges and others almost never report findings of misconduct to state panels and bar associations that are authorized to investigate them.

“In the handful of situations where an investigation is launched,” the report found, “The committees generally failed to properly discipline the prosecutor who committed the misconduct.”

The report concludes with several recommendations on how to improve accountability for prosecutors. It suggests, among other things, that judges ought to mandatorily report all findings of misconduct or error and that state legislatures pass laws requiring prosecutors to turn over all law enforcement material well before trial.

But perhaps most powerful is the report’s introduction, a 2011 letter to then-Attorney General Eric Holder and two national prosecutor associations. It was written in response to the Connick ruling and signed by 19 people whose wrongful convictions were secured in part by prosecutorial misconduct.

“We, the undersigned and our families, have suffered profound harm at the hands of careless, overzealous and unethical prosecutors,” the letter said. “Now that the wrongfully convicted have virtually no meaningful access to the courts to hold prosecutors liable for their misdeeds, we demand to know what you intend to do to put a check on the otherwise unchecked and enormous power that prosecutors wield over the justice system.”

According to the Innocence Project, the Justice Department never responded to the letter.