Prosecutors misbehaved so badly in more than 2,000 cases during that period that appellate judges dismissed criminal charges, reversed convictions or reduced sentences, the study also found.
The study, "Harmful Error," found 223 prosecutors around the nation who had been cited by judges for two or more cases of unfair conduct but only two prosecutors who had been disbarred in the past 33 years for mishandling criminal cases. There are about 30,000 local prosecutors in 2,341 jurisdictions.
A product of three years of research by The Center for Public Integrity, a private ethics watchdog group, the study found 28 cases involving 32 defendants in which judges concluded that misconduct by prosecutors contributed to the convictions of innocent people.
These 32 were later exonerated, 12 of them by use of DNA genetic evidence. Some of these innocent defendants had been convicted of murder, rape or kidnapping; some had been under death sentence before exoneration spared them.
In another 26 cases, 31 innocent defendants were convicted despite their allegations of misconduct by prosecutors. But in those cases, all subsequently exonerated, appellate judges dismissed the misconduct allegations or ruled prosecutors committed "harmless error." DNA evidence exonerated 24 of them.
The report said convictions of an undetermined number of guilty defendants also were undoubtedly overturned because of unfair prosecutor tactics. Some of those defendants could not be retried and were set free, so prosecutor misconduct "has severe consequences for the entire citizenry," the report said.
Charles Lewis, executive director of the center, said that by focusing only on cases in which appellate judges found misconduct the study presented "an extremely conservative and undoubtedly understated picture of the problem." The study also excluded federal prosecutors.
Astoria, Ore., District Attorney Joshua Marquis, a National District Attorneys Association board member, said the cases that were cited emerged "from a universe of millions." The results suggested that the problem was "episodic, not epidemic" and that prosecutors "are and should be subject to a high degree of scrutiny by trial and appellate judges, defendants and defense lawyers, the press and bar associations and ultimately the voters," Marquis added.
Project director Steve Weinberg, a University of Missouri journalism professor on leave, said researchers found and analyzed 11,458 appellate rulings in which prosecutor misconduct was raised as an issue.
In 2,017 cases, appellate judges found misconduct serious enough to order dismissal of charges, reversal of convictions or reduction of sentences. In an additional 513 cases, at least one judge filing a separate concurring or dissenting opinion thought the misconduct warranted reversal.
In thousands more cases, judges labeled prosecutorial behavior inappropriate but characterized it as "harmless error" and allowed a conviction to stand or a trial to continue.
"We are really talking about misconduct in the cases that went to trial," Weinberg told a news conference, noting that, nationally, 95 percent of defendants who are charged never go to trial. A majority plead guilty without a trial; some charges are dropped.
"We eliminated more than 90 percent of all the criminal cases in the United States that could harbor misconduct," because there was no way to detect it, Weinberg said. But Washington University law professor Katherine Goldwasser, a former prosecutor, said it was not safe to assume that "guilty pleas are absent prosecutorial misconduct."
The study found the following types of misconduct:
- Making inappropriate or inflammatory comments in front of the jury.
- Introducing or trying to introduce inadmissible or inflammatory evidence.
- Mischaracterizing evidence or facts to the court or jury.
- Excluding jurors on the basis of race, ethnicity, gender or other discriminatory grounds.
- Making improper closing arguments.
- Hiding, destroying or tampering with evidence, case files or court records.
- Failing to disclose exculpatory evidence.
- Threatening, badgering or tampering with witnesses.
- Using false or misleading evidence.
- Harassing, displaying bias toward or having a vendetta against a defendant or defense lawyer, including denial of speedy trial and selective or vindictive prosecution.
- Improper behavior during grand jury proceedings.
Moss told researchers he was "a hard-hitting but honest prosecutor" who tried more than 400 cases and "obviously ... those convicted are dissatisfied with the outcomes."