A high-ranking police ballistics expert who testified in courts throughout Maryland and neighboring states killed himself after being confronted with evidence that he had lied about his credentials - a revelation that defense attorneys say could force new trials for some of the hundreds of people he helped convict.

Joseph Kopera, head of the Maryland State Police firearms unit, claimed on witness stands to have degrees that he never earned, state police acknowledged yesterday as they began notifying prosecutors and defense attorneys across the region of their findings.

The top prosecutor in Baltimore County and the U.S. attorney for Maryland also said they would review cases that included testimony from Kopera.

Questions regarding the longtime firearms and toolmarks examiner's credentials were raised several weeks ago by state public defenders working with the Innocence Project, a small unit of lawyers who represent defendants they believe have been wrongfully convicted.

Michele Nethercott, chief of the unit, said Kopera not only claimed in court to have degrees he did not earn but also forged at least one document that he offered to the Innocence Project attorneys to justify his qualifications.

"It raises huge red flags, and it's particularly disturbing because he had been doing this for so long that God knows how many cases he's been involved in," Nethercott said yesterday evening in a telephone interview from Annapolis, where she was testifying in favor of a bill that would require oversight of police crime labs in Maryland.

"I mean it's one thing - not that I'm endorsing it - to puff your resume," she said. "But to be coming up with fraudulent transcripts? It does make you wonder what else was going on. It's very, very disturbing, to put it mildly."

State police said that they learned while looking into the circumstances surrounding Kopera's death that defense lawyers had questioned him. Kopera, 61, died from a self-inflicted gunshot March 1- the day his sudden retirement took effect.

A man who answered the door last night at what is believed to have been Kopera's home in Perry Hall declined to comment. Police said Kopera left a suicide note, but they would not describe its contents.

With a career spanning 37 years, Kopera worked on criminal cases in every one of Maryland's 24 jurisdictions as well as in Delaware, Pennsylvania and Virginia and at both the state and federal level, said Col. Thomas E. "Tim" Hutchins, superintendent of the Maryland State Police.

As a firearms examiner - first with the Baltimore Police Department and then the state police - Kopera collected and then analyzed bullets, shell casings, weapons and other forensic evidence. Given the length and breadth of Kopera's work, prosecutors and criminal defense attorneys alike said yesterday that the implications of the investigation could be tremendous, with the analysis of every bullet and every weapon that has passed through Kopera's crime laboratory called into question.

"The potential problem cannot be overstated," said Thomas J. Fleckenstein, a former Anne Arundel County assistant state's attorney, adding that prosecutors around the state will likely be dealing with fallout from the investigation for years.

"Every case he has ever been involved in is open to question," said Fleckenstein, now in private practice. "There will be a lot of prosecutors having a lot of heartburn."

Roland Walker, a veteran criminal defense attorney, said he encountered Kopera on about 50 murder or serious shooting cases over the years and never questioned the firearms expert's credibility.

"He's one of the most compelling experts I've seen in a courtroom - 'experts' in quotes now, that is," he said. "Now," he added, "the question is how much of that was acting and how much was for real. I think I was duped along with hundreds, thousands of other lawyers."

Area prosecutors said they had been told of the discovery. But more than one cautioned that questions about Kopera's testimony in a case would not necessarily be enough to overturn a conviction.

"The question is, what did he claim to have degrees in, and what difference does that make to his qualifications? Obviously, he had taken classes and been sent to specific courses and learned this stuff over the years," said Harford County State's Attorney Joseph I. Cassilly. "Even then, it may not have any real long-lasting effect on some of the cases, especially those that involved experts in other disciplines and other types of evidence. His evidence may have been one piece on the scale of evidence that convicted somebody overwhelmingly."

Some who worked with Kopera said the revelations should not tarnish the decades of careful work he completed on behalf of Maryland law enforcement.

One former city homicide detective said Kopera would come in on his days off to analyze evidence that investigators thought was crucial to making an arrest in a murder case, but wouldn't fudge his analysis, no matter how badly he knew detectives needed a bullet to match a gun to break open a case.