A just legal system doesn’t fear examining wrongful convictions. Pennsylvania’s Supreme Court just made that harder.

As a former U.S. attorney with more than 18 years of experience prosecuting cases involving violent crime, organized crime, and public corruption in Philadelphia, I sought to follow the principle that the role of a prosecutor is to seek justice, not simply convictions, without using improper methods to secure a finding of guilt. This meant following well settled constitutional law requiring prosecutors and law enforcement to identify and turn over to the defense exculpatory evidence and material undermining the credibility of government witnesses prior to trial — no exceptions.

While people accused of crimes are entitled to a fair trial — not a perfect one — the outright failure of prosecutors and law enforcement to comply with the basic rules of fairness undermines public trust in our criminal legal system. More importantly, the failure — whether intentional or negligent — becomes tragic when an innocent person should not have been prosecuted and sentenced in the first place, because the case clearly pointed to another perpetrator who was not prosecuted.

Since 1989, according to the National Registry for Exonerations, more than 3,800 men and women have been exonerated across the U.S. (152 in Pennsylvania) in cases involving the problems just described. Conviction Integrity Units, which have been set up in district attorney offices across the country, including the Philadelphia district attorney’s office, play an important role in addressing the wrongful convictions of innocent people.

Recently, the Pennsylvania Supreme Court — with urging from the Pennsylvania attorney general’s office — issued a ruling that effectively gives the state’s top prosecutor veto authority in any post-conviction relief case in which Philadelphia’s district attorney determines that an innocent person has been convicted and sentenced to prison for a crime they did not commit.

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While I am not in a position as the executive director for the Pennsylvania Innocence Project to comment on the animosity that appears directed at the district attorney, I do know from experience that some prosecutors and law enforcement officers conceal evidence (DNA and other lab test results, contradictory or inconsistent witness statements, evidence of benefits or rewards given to witnesses in exchange for testimony).

Some law enforcement officers use improper methods to coerce statements and false confessions out of people, and some eyewitness identifications are faulty or the product of improper law enforcement influence.

Cooperating witnesses sometimes lie about the involvement of others to avoid responsibility for their own criminality.

And, finally, some criminal defense lawyers are ineffective at their jobs and have no business being in the courtroom when individual liberty is at stake.

If our criminal legal system is truly just, one should not fear looking back to make sure the right person has been held accountable. Victims also lose when prosecutors and police officers get it wrong while the real perpetrator of a crime remains free to victimize others within the community.

There are 67 elected district attorneys in Pennsylvania who are primarily responsible for prosecuting more than 90% of the serious violent crime cases committed within their counties. In Philadelphia County — where police and prosecutorial misconduct are historically known to have resulted in the convictions of innocent men and women — both the Supreme Court and the attorney general appear to support a world in which looking under the hood is a bad thing and needs to be curtailed.

If our criminal legal system is truly just, one should not fear looking back to make sure the right person has been held accountable.

There were exonerations before the current Philly DA, and there will be exonerations after the Philly DA eventually leaves office, because the unfortunate reality is that some prosecutors and law enforcement officers do not play by, or follow, the rules. I know, because during my tenure in the U.S. Attorney’s Office, my colleagues and I prosecuted more than our share of bad police officers who ignored their oath to follow and uphold the law.

While prosecutors, law enforcement officers, and the courts serve an important societal role in holding people accountable for crimes they have committed, they are not perfect.

When it comes to the innocent, we should not be afraid to look back in appropriate cases to make sure that the innocent do not suffer. Both the Supreme Court and Pennsylvania attorney general’s office need to remain mindful of the role of prosecutors and the importance of Conviction Integrity Units to ensure that justice ultimately prevails in our criminal legal system.

Zane David Memeger is the executive director of The Pennsylvania Innocence Project and a former U.S. attorney for the Eastern District of Pennsylvania.