The state made preparations on Wednesday to use a never-tried lethal drug combination to put a man to death for the slaying of a pregnant woman that went unsolved until he inadvertently helped authorities, and the U.S. Supreme Court refused to block the execution.

Dennis McGuire, jailed on an unrelated assault charge, told investigators he had information about the woman's Feb. 12, 1989, death. His attempts to blame the crime on his brother-in-law quickly unraveled, and soon he was accused of being Joy Stewart's killer, prosecutors said. More than a decade later, DNA evidence confirmed McGuire's guilt, and he acknowledged that he was responsible in a letter to Gov. John Kasich last month.

The state planned to execute McGuire on Thursday with a new process adopted after supplies of its previous drug dried up when the manufacturer put it off limits for capital punishment. The two-drug combination has never been used in a U.S. execution.

The state opposed McGuire's last-minute appeal, in which he claimed a jury never heard the full extent of his chaotic and abusive childhood.

"One can scarcely conceive of a sequence of crimes more shocking to the conscience or to moral sensibilities than the senseless kidnapping and rape of a young, pregnant woman followed by her murder," Preble County prosecutors said in a filing with the state parole board last month.

McGuire, 53, was moved from death row in Chillicothe on Wednesday morning to the Southern Ohio Correctional Facility in Lucasville, where executions are carried out. He was calm and cooperative and requested a last meal that included roast beef and fried chicken, prisons spokeswoman JoEllen Smith said.

McGuire spent part of Wednesday visiting with his son, daughter and other family members, Smith said.

His attorneys argue he was mentally, physically and sexually abused as a child and has impaired brain function that makes him prone to act impulsively.

"Dennis was at risk from the moment he was born," the lawyers said in a parole board filing. "The lack of proper nutrition, chaotic home environment, abuse, lack of positive supervision and lack of positive role models all affected Dennis' brain development."

The U.S. Supreme Court gave no explanation in rejecting McGuire's appeal and denying a stay of execution.

The state says similar challenges have failed several times over the decades since Stewart's death.

Documents obtained by The Associated Press show McGuire unsuccessfully sought a reprieve in recent weeks to try to become an organ donor. In November, Kasich, a Republican, granted a death row inmate an eight-month reprieve to let the prison system study his request to donate a kidney to his sister and his heart to his mother. Kasich said McGuire couldn't identify a family member who would receive his organs, as required under prison policy.

Ohio officials planned to use intravenous doses of two drugs, the sedative midazolam and the painkiller hydromorphone, to put McGuire to death. The method has been on the books as the backup method since 2009 but never had to be used.

McGuire's attorneys say he is at substantial risk of a medical phenomenon known as air hunger, which will cause him to experience terror as he strains to catch his breath.

The state presented evidence disputing the air hunger scenario and saying McGuire waited far too long to file the appeal, which came this month.

A federal judge sided with the state and said the execution can proceed. At the request of McGuire's lawyers, Judge Gregory Frost on Wednesday ordered the state to photograph and then preserve the drugs' packaging boxes and vials and the syringes used in the execution.