As of the date of this post, 3,735 people in the U.S. have been exonerated after spending a combined 34,704 years in prison for crimes they didn’t commit. Sadly, that number continues to grow every year, leaving thousands of people waiting for justice.

Why do wrongful convictions happen? Rarely because of one mistake. More often, it’s a perfect storm. The leading cause may surprise you. According to the National Registry of Exonerations, the leading cause of wrongful convictions is perjury and false accusations, which account for 64% of cases. Close behind is official misconduct at 61%. Other causes include false or misleading forensic evidence (29%), mistaken IDs (27%), and false confessions (13%). Many of those, too, are tied to misconduct — suggestive lineups, coercive interrogations, or pressure to secure convictions.

Consider James Davis, the first exoneration won by Legal Aid’s Wrongful Conviction Unit. He was falsely identified by a jealous ex-girlfriend. Or the case of Fernando Bermudez, where the witness was pressured by law enforcement to claim he was the shooter. Both men were condemned by testimony prosecutors knew — or should have known — was untrue.

Prosecutors are supposed to prevent this. They aren’t just advocates; they’re public officers sworn to ensure justice. Therefore, in the role of public office, “a prosecutor owes a duty of fair dealing to the accused and the courts”. That duty is violated when the prosecutor obtains a conviction based on evidence they know, or should know, to be false.

Prosecutors are supposed to prevent this. They aren’t just advocates; they’re public officers sworn to ensure justice.

But reality often falls short. In Bermudez’s case, the main witness originally described the shooter as “Luis” or “Lou,” a Puerto Rican man from W. 92 Street. Bermudez is Dominican, from Inwood, and went by “Most.” Despite the glaring mismatch, police showed the witness Bermudez’s photo, and the story shifted. By trial, it had shifted again. The prosecutor allowed the contradictions to stand. At 22, Bermudez was sentenced to 23 years to life. He served nearly 18 years before the judge found that Mr. Bermudez was innocent of all charges.

In another case, a witness, seeing the defendant being led in handcuffs to court, told the prosecutor — just before testifying — that she had the wrong man. She knew the real shooter and was even caught on video with him the night of the crime. Instead of alerting the court or defense, the prosecutor told her the defendant must have changed his appearance. The trial went forward. The client was convicted. The prosecutor was promoted.

These are not outliers. They show a pattern: prosecutors relying on testimony they know or should know is false, and rarely being held to account.

ProPublica examined 30 New York cases overturned for prosecutorial misconduct. Only one prosecutor was disciplined. None were disbarred or suspended. Many were promoted. Meanwhile, 2,278 people have been imprisoned because of misconduct, losing a collective 21,169 years of their lives.

Prosecutors like to say misconduct is rare. The evidence says otherwise. And until prosecutors face real consequences for using or tolerating false testimony, wrongful convictions will continue — along with the human cost.

Elizabeth Felber is the Supervising Attorney of The Legal Aid Society’s Wrongful Conviction Unit.