A federal appeals court has overturned the federal sexual abuse convictions and life sentences of an Oklahoma man who was at the center of a U.S. Supreme Court ruling on tribal sovereignty.

The 10th U.S. Circuit Court of Appeals on Tuesday ruled that jury instructions regarding inconsistent statements by key witnesses against Jimcy McGirt during his trial on charges of abusing a 4-year-old girl in 1996 were incorrect.

The trial court judge instructed the jury that testimony by the girl, her mother and her grandmother during the federal trial that was not consistent with their testimony during the original trial in 1997 could only be used to consider the witnesses’ credibility, not whether they were testifying truthfully.

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The testimony included inconsistencies in whether the then 4-year-old was coached on what to say by her mother and the girl's behavior toward McGirt just before and after the alleged abuse.

The appeals court rejected prosecutors' assertion the error was harmless, saying the testimony was crucial because there was no physical evidence of abuse. A pediatrician had testified there was no evidence of sexual assault of the girl but said the finding was not conclusive.

"Contrary to the government’s argument, the verdict here was not 'supported by overwhelming evidence,'" the court wrote.

The ruling sends the case back to U.S. District Court and does not address the 2020 tribal sovereignty ruling in which the U.S. Supreme Court reversed the state child molestation convictions of McGirt because he is Native American and the crime occurred on a tribal reservation that was never disestablished by Congress.

Assistant U.S. Attorney Jarrod Leaman declined comment on any potential impact on the tribal sovereignty ruling, saying prosecutors are focused only on the criminal aspect of the case.

"In the next week or two we're going to evaluate the case, evaluate the ruling ... we're going to consult with the victim's family" before deciding whether to appeal further, Leaman said.

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The 2020 McGirt ruling found that the state has no authority to prosecute major crimes committed on tribal land by Native Americans. That authority rests with federal or tribal prosecutors, the court ruled at the time.

McGirt, 74, was given life without parole and two 500-year prison sentences following his convictions on state charges of rape, lewd molestation and sodomy.

Months after the Supreme Court's ruling overturned the state convictions, McGirt was convicted in federal court on two counts of aggravated sexual abuse and one count of abusive sexual contact and sentenced to life in prison.

He currently remains in federal custody.