Empty bullet casings at the National Armory gun store and gun range in Pompano Beach, Fla. (Lynne Sladky/AP)

Claims that forensic experts can match a bullet or shell casing found at a crime scene to a specific weapon lack a scientific basis and should be barred from criminal trials as misleading, a D.C. Court of Appeals judge wrote this week.

The opinion, by Associate Judge Catharine Easterly, is not binding on criminal prosecutions in D.C. Superior Court, where firearms and ballistics evidence have been introduced in scores of violent felony cases in recent years. But it continues a nationwide push for heightened scrutiny of forensic techniques and testimony relied upon in thousands of criminal convictions.

Easterly’s opinion came in response to an appeal brought by Marlon Williams, 36, of Southeast Washington. He argued that his murder conviction in the 2010 fatal shooting of Min Soo Kang, 37, of Fairfax County should be overturned because, among other things, a D.C. police forensics expert improperly declared a “unique” match between bullet slugs recovered from the victim’s car and a handgun found in Williams’s bedroom.

“Those markings are unique to that gun and that gun only,” Luciano Morales testified, according to court filings. “Item Number 58 fired these three bullets,” he told the jury, referring to the handgun by its trial exhibit number.

Prosecutors with the U.S. attorney’s office for the District called the error “regrettable,” acknowledging in 2011 court filings that forensic practitioners should not state conclusions to an “absolute” or “100% scientific certainty.” Prosecutors also told the Court of Appeals that the policy barring those 100 percent conclusions in firearms examination cases­ had been in place since about 2009, predating the testimony delivered at Williams’s trial.

The error “is more than regrettable. It is alarming,” Easterly wrote in a concurring opinion to the decision of the three-judge panel published Thursday.

Easterly likened claims of a one-to-one match of bullet to gun to “the vision of a psychic,” a statement of “foundation­less faith in what he believes to be true.”

“To uphold the public’s trust, the District of Columbia courts must bar the admission of these certainty statements,” Easterly wrote. “We cannot be complicit in their use.”

Because Easterly’s statement was delivered in a concurring opinion, it does not carry the force of law. Easterly noted that only one state supreme court, in Massachusetts, and no U.S. Court of Appeals expressly limits testimony by firearms examiners, despite extraordinary criticism of its validity from legal scholars.

At trial, Williams’s defense lawyer at the time, failed to object to the testimony from Morales.

Absent that objection, Easterly — a former public defender appointed by President Obama to the D.C. Court of Appeals in 2011 — wrote, “We could only reverse if the law were clear that the expert could not make these statements.” District law does not have that clear prohibition, she said, “but it should.”

Williams failed in his bid to have his conviction overturned, with Easterly writing a majority opinion joined by Associate Judge Phyllis D. Thompson and Senior Judge Frank Q. Nebeker.

Easterly’s opinion comes as a national commission appointed by Obama to improve forensic science in the criminal-justice system weighs whether to recommend far-reaching changes­ to some forensics.

In her concurring opinion, Easterly noted that the policy shift that prosecutors tracked to about 2009 came after two National Research Council panels reported in 2008 and 2009 that there is no statistical basis to determine how often bullets fired by different weapons might look alike, or even whether a firearm makes a unique, reproducible mark.

Many scientists also have questioned the reliability of other identification claims made based on subjective analysis of hair samples, bite marks, burn patterns or firearms. Such pattern-based forensic analysis and testimony have long been admitted by courts and championed by law enforcement officials, who say when performed and described correctly, they can yield valuable evidence.

In an interview, Williams’s attorney for the appeal, Enid Hinkes, said, “Judge Easterly’s concurring opinion is an accurate statement of the science — or the lack of it. But, unfortunately, it was not translated into action.”

Hinkes said she intends to seek a hearing before the full appeals court for Williams, who is at the U.S. Penitentiary Hazelton in Bruceton Mills, W.Va.

Bill Miller, a spokesman for the U.S. attorney’s office, said it is reviewing the ruling and had no comment beyond what the office stated in its court filings.

In court papers, prosecutors said pattern-matching remains widely accepted by scientific practitioners and courts.

Current policy calls for testifying to matches on bullet-gun markings “to a reasonable degree of scientific certainty,” not to an absolute certainty. Morales’s testimony violated that policy, prosecutors said in their appeals court files, but said the error was harmless given the evidence in the case.

The office declined to provide information about often such errors in testimony occur or about how it enforces the policy.