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DULUTH – An attorney for the Chisholm man convicted for the long unsolved murder of Nancy Daugherty appealed to the Minnesota Supreme Court, challenging the way his DNA was examined and the district court's denial of his alternate perpetrator defense in his trial.

Michael Carbo, 55, was found guilty of first-degree murder while committing a sexual act in August 2022 — a resolution to a decades-old Iron Range cold case. Daugherty was found strangled in her Chisholm home in summer 1986. Carbo had continued to live quietly in the town of 4,900 and is the only person who has ever been arrested in connection with the murder.

Earlier this week, Assistant State Public Defender Adam Lozeau argued that Carbo should have been able to introduce evidence in St. Louis County Court that pointed to another suspect — a man that Daugherty had spent time with hours before she was killed. That man, who she had dated in the past, had sent her several letters indicating that he still had romantic feelings for her. He made romantic overtures the night Daugherty died, and doubled back to her house once more after she asked him to leave.

His hair was found in Daugherty's home.

At one point, the man — who was a witness for the state during Carbo's trial — told an investigator: "I've often wondered 'Jeez. Did I wake up in the middle of the night, drive over there and kill her?'"

"The jury didn't hear this evidence because the court prohibited the jury from hearing it," Lozeau told the justices. "This did not just prevent relevant evidence from being presented for jurors' consideration, it gave the jurors an actively misleading representation of the state's key witness and his relationship with the victim."

This kept Carbo from presenting a complete defense, Lozeau said.

Assistant Attorney General Peter Magnuson responded that the district court "exhaustively addressed" the use of an alternate perpetrator defense.

"Which leaves little room for this court to reverse for an abuse of discretion," he said.

Associate Justice Paul Thissen ran through the list of ways the man was connected to Daugherty — including the fact that his truck might have been spotted in front of her house that night — and pointedly addressed Magnuson.

Would that be enough for probable cause, to bring charges against him? Thissen asked.

Magnuson paused.

"This goes to the constitutional fairness of the thing, and so I'd like you to answer it and not dodge it," Thissen said.

Associate Justice G. Barry Anderson agreed.

"Why isn't that enough?" he asked. "And if this isn't enough, I think there's a question about whether or not anybody gets to an alternate perpetrator defense."

The Star Tribune generally does not name suspects unless they have been charged.

In 2020, Chisholm Police Chief Vern Manner contacted a company that uses public genealogy databases to whittle down a suspect's family tree. They found a match with a distant relative of Carbo's, who had offered up a sample to a genealogy database.

Lozeau argued that the deep analysis done on the semen Carbo left at the crime scene on Daugherty's fingernails violated his Fourth Amendment rights — protecting him from unreasonable search and seizures.

Law enforcement used the sample to identify a suspect — and more, Lozeau said. It was used to create a full profile of information about Carbo before he was even on law enforcement officials' radar.

"His ancestors dating back hundreds of years, it predicts what his physical characteristics would be — it was used to create a picture of him, what he looked like at age 25," he said.

Magnuson responded that Carbo abandoned the DNA evidence at the scene without any expectation of privacy and that technological advances in this sort of testing are to be celebrated, not feared.

Justice Natalie E. Hudson said the court's decision would be offered up "in due course."

Carbo received a life sentence, but can petition for parole after 17 years from his sentencing. He served two years in the St. Louis County Jail before his trial and is currently an inmate at the Minnesota Correctional Facility in Rush City.

Correction: An earlier version of this story misidentified Justice Natalie Hudson.