AUBURN – The state’s high court has overturned the conviction of a Lewiston man found guilty last year of robbing a variety store clerk at knife point.

The Maine Supreme Judicial Court ruled that Vinson Mangos, 34, should have been able to question the chemist who helped prepare clothing found near the crime scene that was later linked to him through DNA analysis.

A new trial is expected to be scheduled for December, a clerk at Androscoggin County Superior Court said Tuesday.

Mangos was indicted by an Androscoggin County grand jury on a count of robbery and later convicted by a jury. He was sentenced to 18 years with all but eight years suspended, plus six years of probation.

A judge allowed DNA evidence to be introduced at Mangos’ trial purporting to link him to the robbery without requiring prosecutors to establish “sufficient foundation.” The judge also didn’t give Mangos the opportunity to cross-examine a chemist from the Maine Crime Laboratory who created three swabs from discarded clothing police collected near the crime scene, the court wrote. The chemist didn’t appear at the trial. The swabs were analyzed by a different crime lab worker who did testify at the trial. A supervisor testified about how the swabs were created and referred to a report prepared by the missing chemist.

“It was totally a chain of evidence thing,” Assistant District Attorney Craig Turner said. He said the state expects to retry Mangos and will seek to have the now-former crime lab worker appear at his trial next time to testify about her role in preparing the swabs from the clothing for analysis.

A bandanna and T-shirt apparently worn by the robber were found at the scene and turned over by police to the crime lab where at least three workers were involved in processing that evidence.

During the trial, Robert Ruffner, attorney for Mangos, repeatedly objected to testimony regarding the DNA evidence, the high court’s ruling said. In his appeal, Mangos argued the state didn’t demonstrate clearly at trial that the swabs linked to him were taken from clothing found at the scene, because one of the people who handled that evidence didn’t take the witness stand. The defense would have questioned that worker, Nancy Keune, to determine whether she followed proper scientific methods during her preparation of the evidence for later DNA testing by Erin Miragliuolo, a forensic DNA analyst, the appeal said.

“The only way … that the court could conclude that the DNA evidence presented at trial came from the clothing found near the scene of the robbery, and thus was relevant, was for the court to infer that Keune properly created the DNA swabs by taking them from those articles of clothing. Such a substantial factual gap between the receipt by Keune of the clothing and the testing by Miragliuolo reflects more than a minor break in the chain of custody,” the court’s ruling said.

Moreover, no one witnessed Keune remove the DNA material from the clothing found near the crime scene that would have established a foundation for the admission of the DNA evidence, the court’s ruling said.

Mangos argued and the high court agreed that his Sixth Amendment rights were violated because the state didn’t make Keune available for questioning about the protocols she followed.

Writing for the Maine Supreme Judicial Court, Justice Clifford concluded that he and his colleagues couldn’t conclude “to a high probability” that the admission of the DNA evidence at Mangos’ trial didn’t affect the jury’s verdict.

Ruffner said Tuesday that the court “made the right decision under the facts and the law.” His court-appointed client had seen the high court’s ruling, Ruffner said.