Oklahoma man sentenced to death twice set to be executed OKLAHOMA CITY (Reuters) - A convicted Oklahoma killer who was spared execution once but asked for a new trial and was sentenced to death a second time is set to be put to death on Tuesday. Michael B. Selsor was convicted of killing a Tulsa convenience store clerk in 1975. After he was sentenced to death, the U.S. Supreme Court ruled in 1976 that Oklahoma's capital punishment law was unconstitutional and his sentence was modified to life in prison. While Oklahoma's death penalty was in limbo, the state's criminal appeals court decided former death row inmates whose sentences were modified would not face the death penalty again should they win new trials. Selsor sought a new trial and received one in 1998. But again he was found guilty and sentenced to death. The Oklahoma Court of Criminal Appeals overruled one of its earlier rulings affecting inmates like Selsor, opening the death penalty option at his new trial, according to one of his lawyers Gary Peterson. "It's a tragic story," Peterson said. He just had the legal rug pulled out from under him. Selsor appealed but was told him he had no right to be warned that Oklahoma law could be changed to make him eligible for the death penalty at his second trial, Peterson said. His execution would be the 18th in the United States this year and the third in Oklahoma, according to the Death Penalty Information Center.