For years, firearms expert Joseph Kopera helped convict defendants across Maryland.

He would show up to trials with his oversized wooden model of a bullet to explain how projectiles pick up specific markings as they’re fired through specific guns.

“Like fingerprints,” he would say.

Kopera could explain all things ballistics — shell casings, firing pins, shotgun blasts — and during his tenure with the Maryland State Police forensics division from 1991 to 2007 testified in hundreds of cases.

“He was fabulous in front of a jury,” said Montgomery County State’s Attorney John McCarthy.

This fall, though, state police officials discovered something else: In at least some of his lab documents, Kopera forged the initials of a co-worker who ostensibly reviewed his work. The revelation has prompted the state police to launch a review of 4,041 Kopera case files for faked signatures and other possible shortcuts.

Exactly how often Kopera did this is not known. Nor is there any way to gauge whether the errant signatures will lead to overturned convictions, new trials or people set free.

The agency has been notifying prosecutors and defense attorneys about their initial findings. Police emphasized that so far, all they’ve seen is false signatures, not false firearms examinations.

Defense attorneys are concerned.

“In our view, every case of his becomes suspect because this just goes to the heart of his credibility,” said Becky Feldman, the second-ranking attorney at Maryland’s public defender’s office.

The signature issues are not the first problems found in Kopera’s work. Twelve years ago, attorneys from Maryland’s Innocence Project discovered he lied about his credentials on witness stands — claiming degrees he did not have. On March 1, 2007, as these problems were surfacing, Kopera fatally shot himself, according to Maryland court records.

This fall, in a sampling of 32 verification cases in which Kopera had matched a piece of ammunition to a weapon, or a piece of ammunition to another piece of ammunition, he forged initials at least six times, according to state police.

State police are conducting their review in two phases.

In the first, underway now, forensics officials are breaking out the 4,041 cases by jurisdictions so they can inform local prosecutors of all their “Kopera cases.” In the second phase, forensics officials hope to tell local prosecutors of any specific cases that have forgeries or procedural errors.

“Nobody wants to hide the ball here,” said McCarthy, the Montgomery state’s attorney.

Prosecutors say they will contact those who were convicted and defense attorneys.

“We’re trying to make sure everybody knows what happened,” added Brian DeLeonardo, president of the Maryland State’s Attorneys’ Association.

Kopera began his career at the Baltimore City Crime Lab, where he spent 21 years, according to court records. In 1991, he joined the Maryland State Police forensics division, which analyzes cases throughout the state, according to court and state police documents.

By 1994, according to court records, Kopera was testifying in court two or three times a week. McCarthy remembered bringing him into court and ushering him to the witness chair.

“He’d politely ask the judge: ‘May I step down?’ The judge would say yes, and Joe would walk down to the well of the courtroom, explaining lands and grooves and striations,” McCarthy said of how gun barrels leave specific marks on bullets.

In a case in Howard County, Kopera walked about the courtroom pumping a menacing-looking shotgun to explain the path of exiting projectiles, according to an article about him in the Baltimore Sun.

In time, Innocence Project attorneys began looking into his background, specifically the claims that he had earned degrees from the Rochester Institute of Technology and the University of Maryland. When they confronted Kopera, he gave them a forged transcript from U-Md., according to court records.

The revelations from the Innocence Project resulted in multiple attempts to challenge convictions based on the theory that Kopera’s willingness to lie about his credentials constituted “new evidence” in a case. A standard test then developed in Maryland’s courts: If Kopera had not testified at a particular trial, is there a “substantial or significant possibility” the verdict would have been different?

That test, among other factors, has made getting new trials in Kopera cases difficult, said Michele Nethercott, a longtime attorney with Maryland’s Innocence Project. And she is skeptical the new revelations will make it much easier.

“I’m not saying that forgeries aren’t disturbing conduct,” Nethercott said. “I just don’t think the conduct — in and of itself — is going to result in very many defendants getting their convictions overturned.”

Kopera’s actual lab work, prosecutors have long said, has always held up as accurate.

Still, in Montgomery County, McCarthy said, challenges probably would again depend on how strong the rest of the evidence was compared with Kopera’s contribution. If Kopera’s testimony was essential, McCarthy said, prosecutors may have to see whether the actual weapons and ammunition from cases are still stored in evidence rooms. If so, he said, perhaps they could be analyzed again.

“If you could retest and verify what Joe did, you might try to do that,” McCarthy said.

Alternately, Kopera’s case files may have photographs of his lab work, which could be reviewed by an outside examiner, according to McCarthy.

But neither analysis might be possible.

“If that’s the case, and if Joe’s testimony was crucial, you could have some problems maintaining a conviction,” McCarthy said.

Defense attorney Daniel Wright has tried for years to overturn the conviction of Mark French, who is serving a life sentence after being convicted in 1994 of attempted murder in the shooting of a police officer.

Kopera testified in French’s case, linking bullets recovered from the officer’s body with a gun found in the same residence where French was arrested.

Wright’s efforts have fallen short, according to court records. A judge ruled in 2018 that other evidence — including a witness who said French told her “it was either me or him — was strong enough to convict French regardless of Kopera’s testimony.

The newly discovered forgeries, Wright said, give him a broader line of attack. He said that judges should consider how jurors would have reacted to learning that a witness — called by prosecutors — had doctored lab signatures.

“That’s a lot more than résumé padding,” Wright said. “It could have colored how jurors felt about the entire case.”