WASHINGTON (NEXSTAR) - In a high-profile death penalty case, the Supreme Court is weighing whether to throw out the murder conviction of an Oklahoma death row inmate. The state's appeals court has upheld the sentence.  Lawyers for the state of Oklahoma say death row inmate, Richard Glossip, didn't get a fair trial.  "It's not every day that an attorney general confesses error," said Paul Clement, the attorney representing Oklahoma's Attorney General.  A jury convicted Glossip of arranging the 1997 murder of his former boss Barry Van Treese. Oklahoma Republican Attorney General Gentner Drummond says recent evidence of prosecutorial misconduct warrants a new trial. "I'm not saying he's not guilty. But I am saying he was not afforded due process rights," Drummond said.  Years after Glossip's conviction, the state said it did not disclose that their key witness lied on the stand by denying being treated for a psychiatric condition.  "Your one witness has been exposed as a liar," Justice Elena Kagan said during the hearing.  "The whole case depended on his credibility," Justice Brett Kavanaugh said.  Now almost 30 years since the crime, the family of the murder victim is here at the Supreme Court asking justices to uphold the conviction.  "If you'd told me at 16, when this happened, I'd still be dealing with this at 44, I wouldn't have believed you," Derek Vaan Treese said.  Derek Van Treese was a teenager when his father was beaten to death with a baseball bat at the motel he owned. He wants to see the death sentence upheld.  "We've been through the entire emotional gamut of frustration and anger and grief," Van Treese said.  The lawyer defending the state's criminal appeals court, which has upheld the sentence, argues the Supreme Court shouldn't be deciding this state issue and instead:  "dismiss this case for lack of jurisdiction, leaving petitioner free to pursue state law clemency or other available relief," said Christopher Michel, the lawyer representing Oklahoma's lower court decision.  The court is expected to have a decision next summer.