OKLAHOMA CITY: A death row inmate's scheduled execution for his role in a 1997 motel killing would be the first in Oklahoma since the nation's highest court upheld the state's three-drug lethal injection formula.

Unless the US Supreme Court halts the execution, Richard Glossip is scheduled to receive a lethal injection at 3 p.m. CDT Wednesday at the Oklahoma State Penitentiary in McAlester, despite his claim of innocence. A request for a stay of execution is pending with the US Supreme Court.

Glossip was the lead plaintiff in a separate case in which his attorneys argued the sedative midazolam did not adequately render an inmate unconscious before the second and third drugs were administered. They said that presented a substantial risk of violating the Eighth Amendment prohibition on cruel and unusual punishment. But in June, the justices voted 5-4 that the sedative's use was constitutional.

Glossip was convicted of orchestrating the beating death of Barry Van Treese, the owner of the Oklahoma City motel where Glossip worked. But Glossip claims he was framed by the actual killer, Justin Sneed, who is serving a life sentence and was the state's key witness against Glossip in two separate trials.

Just hours before Glossip was originally to be put to death on Sept. 16, the Oklahoma Court of Criminal Appeals granted a two-week reprieve to review his claims of new evidence in the case, including another inmate's assertion that he overheard Sneed admit to framing Glossip.

But in a 3-2 decision earlier this week, the same court denied Glossip's request for an evidentiary hearing and emergency stay of execution, paving the way for his execution to proceed. The Court of Criminal Appeals' majority wrote that the new evidence simply expands on theories raised in his original appeals.

On Tuesday, Glossip's attorneys made a last-ditch request to both the US Supreme Court and Oklahoma Gov. Mary Fallin to issue a stay of execution.

"Recently discovered evidence demonstrates substantial doubt about Sneed's credibility," his attorneys wrote in a petition to the Supreme Court.

Fallin has repeatedly denied Glossip's request for a 60-day stay of execution and said in a statement Tuesday she has no plans to stop the punishment.

"The state of Oklahoma has gone to extraordinary lengths to guarantee that Richard Glossip is treated fairly and that the claims made by him and his attorneys are taken seriously," Fallin said. "He has now had multiple trials, seventeen years of appeals, and three stays of his execution. Over and over again, courts have rejected his arguments and the information he has presented to support them."

Oklahoma first used midazolam last year in the execution of Clayton Lockett, who writhed on the gurney, moaned and clenched his teeth for several minutes before prison officials tried to halt the process. He died 43 minutes after the sedative was first injected.

The state then increased by five times the amount of midazolam it uses and executed Charles Warner in January. He complained of a burning sensation but showed no other obvious signs of physical distress.

Oklahoma has two more executions planned in upcoming weeks. Benjamin Cole is set to be executed on Oct. 7 for the 2002 killing of his 9-month-old daughter, and John Grant is scheduled to die on Oct. 28 for the 1998 stabbing death of a prison worker at the Dick Connor Correctional Center in Hominy.