Oklahoma Attorney General Gentner Drummond is expected to ask the state's pardon and parole board to consider clemency for death row inmate Richard Glossip.

Glossip, 59, who has spent 25 years in prison for his conviction in the 1997 murder of motel owner Barry Van Treese and maintains his innocence to this day, has been just hours away from his execution three separate times and is scheduled to face death again on May 18. 

"I am not aware of any Oklahoma Attorney General ever supporting a clemency application for a death row inmate. This is for good reason," Drummond said in a Monday letter. "In every previous case that has come before this Board, the State has maintained full confidence in the integrity of the conviction. That is simply not the case in this matter due to the evidence that was not disclosed to the jury."

That evidence includes false testimony from the state's star witness in Glossip's trial and conviction, Justin Sneed, who "confessed to murdering [Van Treese] and was able to avoid the death penalty himself only by testifying that Mr. Glossip paid for the murder," Drummond explained in his letter.

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Richard Glossip's execution is scheduled for Sept. 25.

Oklahoma death row inmate Richard Glossip is facing his fourth execution date on May 18. (Oklahoma Department of Corrections via AP File)

"Based on the complete record… it would represent a grave injustice to execute a man whose trial conviction was impugned by a litany of errors, that when taken in total would have created reasonable doubt," Drummond wrote. "No execution should be carried out under such questionable circumstances."

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Glossip was sentenced to death for Van Treese's murder. Prosecutors allege Glossip killed Van Treese, the owner of a motel where Glossip worked as a manager, by convincing a 19-year-old maintenance worker, Justin Sneed, to execute his killing.

Oklahoma County District Attorney David Prater to respond to the petition to review Richard Glossip's case.

Oklahoma death row inmate Richard Glossip, 59, has spent 25 years in prison for his conviction in the 1997 murder of motel owner Barry Van Treese and maintains his innocence to this day. (Fox News Digital)

The death row inmate was just hours away from his execution in 2015 when prison officials realized they did not have the right lethal drug and were forced to delay his death date.

DEATH ROW INMATE RICHARD GLOSSIP'S FOURTH EXECUTION DATE SET AS LAWMAKERS SEEK NEW HEARING TO PROVE INNOCENCE

Sneed was sentenced to life after pleading guilty to beating Van Treese to death with a baseball bat in 1997 in a room at the Oklahoma City motel. Sneed testified that he killed Van Treese but only after Glossip, the motel manager, promised to pay him $10,000 to commit the crime. But Glossip's attorneys argue that his murder-for-hire conviction and death sentence are unsubstantiated. 

The Reed Smith law firm recently released a 340 report detailing new evidence in Richard Glossip's case

Richard Glossip was hours away from his execution in 2015 when prison officials realized they did not have the right lethal drug and were forced to delay his death date. (Fox News Digital)

Glossip's attorneys argue Sneed, who has been sentenced to serve life in prison, is Van Treese's "real killer."

More than 60 Oklahoma lawmakers, including dozens of pro-death-penalty Republicans, have called for a new trial for Glossip.

OKLAHOMA DEATH ROW INMATE'S CASE TO BE REVIEWED BY OUTSIDE LAW FIRM AFTER LAWMAKERS RAISE DOUBTS ABOUT HIS GUILT

Last week, however, the Oklahoma Court of Criminal Appeals upheld his conviction after his attorneys requested a new trial.

READ AG DRUMMOND'S LETTER HERE:

"Oklahoma’s elected Attorney General Gentner Drummond found, after conducting his own independent review, that the State’s star witness against Mr. Glossip, Justin Sneed, was not a truthful witness," Glossip's attorney, Don Knight, said last week. "Without Sneed’s ‘material misstatements’ the outcome of Mr. Glossip’s trial would have been different. Since the State now agrees that the only witness to allege that Mr. Glossip was involved in this crime cannot be believed, it is unconscionable for the court to attempt to force the State to move forward with his execution."

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The Oklahoma Pardon and Parole Board will hold a hearing regarding Glossip's conviction on Wednesday at 9:30 a.m. CT.