The U.S. Supreme Court on Tuesday declined to halt the looming execution of a convicted murderer who claimed that his attorneys' flat-fee contracts incentivized them to push him to plead guilty before they secured promises from prosecutors not to pursue a death sentence.

Brian Joseph Dorsey, a former drug addict who was convicted of shooting his cousin Sarah Bonnie and her husband Ben Bonnie in their sleep, is slated to be executed at 6 p.m. CDT by lethal injection at Eastern Reception, Diagnostic and Correctional Center, in Bonne Terre, Missouri.

Dorsey's current attorneys claimed he was experiencing drug-induced psychosis when he committed the murder, and said his two trial attorneys, who were each hired by the state through $12,000 flat-fee arrangements, did almost nothing to present mitigating evidence, such as his struggle with depression and substance addiction, that would have helped him avoid a death sentence.

But Justice Brett Kavanaugh dashed Dorsey's hopes Tuesday. In a couple of orders, he denied his two petitions for certiorari, one challenging the flat-fee contracts as creating a conflict of interest that were detrimental to his defense, and one challenging the execution as unnecessary given Dorsey's apparent rehabilitation behind bars.

In his last statement before his execution, Dorsey expressed remorse.

"To all of the family and loved ones I share with Sarah and to all of the surviving family and loved ones of Ben, I am totally, deeply, overwhelmingly sorry. Words cannot hold the just weight of my guilt and shame. I still love you. I never wanted to hurt anyone. I am sorry I hurt them and you," he said. "To all those on all sides of this sentence, I carry no ill will or anger, only acceptance and understanding."

On Monday, Missouri Gov. Michael L. Parson, a Republican, had denied a request to commute Dorsey's death sentence to life in prison without possibility of parole, despite broad support for clemency, including from correctional officers who described Dorsey as a "good guy" who "doesn't deserve to be executed."

"Executing Brian Dorsey is a pointless cruelty, an exercise of the state's power that serves no legitimate penological purpose," Assistant Federal Public Defender Kirk J. Henderson said in a statement Tuesday afternoon. "My heart goes out to the many family members and friends who love Brian, and to the dedicated men and women of the Missouri Department of Corrections, who have seen the goodness he is committed to bringing to the world. We will miss his smile and his bear hugs. It has been my honor to know Brian and to share his story."

If the execution moves forward, Dorsey will be the first person Missouri puts to death this year. The state executed four people last year.

Dorsey's clemency petition enjoyed broad and diverse support. In a letter to Parson, a group of 72 former and current correctional officers who had interacted with Dorsey throughout his 18-year incarceration described him as a role model prisoner who never got into trouble and worked for a decade as the prison's barber.

"We know that he was convicted of murder, but that is not the Brian Dorsey that we know," they said.

Five of the 12 jurors who voted to send Dorsey to death as well as Michael A. Wolff, who sat on the Missouri Supreme Court that upheld the sentence, had also asked the governor to spare his life.

But on Monday, Parson, who since taking office has not used his power under the state's constitution to unilaterally grant clemency to people on death row, said Dorsey's death sentence was found to be appropriate by jurors and courts, and that he deserved to be killed "for his heinous crimes."

"Dorsey murdered his cousin, Sarah Bonnie, and her husband, Ben Bonnie, in the middle of the night after they rescued Dorsey from drug dealers attempting to collect debts at Dorsey's apartment earlier in the day. After he murdered them, Dorsey raped Sarah's corpse as the Bonnies', now-orphaned, four-year-old daughter slept in another room," Parson said. "The pain Dorsey brought to others can never be rectified, but carrying out Dorsey's sentence according to Missouri law and the court's order will deliver justice and provide closure."

The Office of the Missouri Attorney General declined to comment Tuesday.

Tim Lancaster, a retired Missouri Department of Corrections officer and investigator who worked for 27 years at Potosi Correctional Center in Mineral Point, Missouri, which hosts the state's death row, said in a statement Tuesday that he believed that Dorsey feels "deep shame and remorse" for his crime and that his execution "doesn't make sense."

"I believed that the whole purpose of 'corrections' was to rehabilitate people. I knew Brian Dorsey for many years, and I can say without hesitation that he was completely rehabilitated," Lancaster said. "He was a good person who made a mistake and was working to do better. I thought that was what we hoped for by sending people to prison."

As Dorsey's execution date closed in, attorneys with the Office of the Federal Defender and the MacArthur Justice Center pursued all legal avenues available to him. On Saturday, the attorneys announced reaching a settlement, the details of which are not public, that ended a suit challenging the state's execution protocols.

"The Missouri Department of Corrections has agreed to resolve Mr. Dorsey's challenge to the lethal injection protocol by adding safeguards that will reduce the risk of undue pain and suffering and protect Mr. Dorsey's right to meaningfully engage in prayer and last rites with his spiritual advisor during the execution process," Assistant Federal Public Defender Arin M. Brenner said in a statement Saturday.

Jenni Gerhauser, a cousin of both Dorsey and Sarah Bonnie, said in a statement on Tuesday afternoon that her family was "devastated and disheartened" by the failure to save his life.

"We are not so blinded by our love for him that we don't understand that he was convicted of committing a terrible crime against someone we loved just as deeply as we do Brian, but nor are we capable of rewriting history to convince ourselves that Brian still isn't the same loving, compassionate, helpful person he always was," she said. "We know that if he had been in control of his thoughts and actions whatsoever, none of us would be in this position today. Anyone who believes otherwise doesn't truly know Brian."

Gerhauser added: "The death penalty isn't punishment for the convicted. This evening, Brian will be set free. His punishment will end, and for all of us only guilty of loving him, ours will begin. That is not the life sentence we sought."

--Editing by Adam LoBelia.

Update: This story has been updated with Dorsey's final statement.