Benjamin Cole, who was executed Thursday, is seen in this undated photo from the Oklahoma State Department of Corrections.
CNN  — 

Oklahoma has executed by lethal injection Benjamin Cole, who was sentenced to death for the 2002 murder of his 9-month-old daughter Brianna Victoria Cole, over the objections of defense attorneys who argued the 57-year-old suffered from schizophrenia and was severely mentally ill.

The case highlighted a longstanding issue in the debate over capital punishment: how it should apply to those who suffer from mental illness. Meanwhile, relatives of the slain infant on Thursday decried the two-decade span between Brianna’s death and Cole’s execution.

The execution – the second of 25 Oklahoma has scheduled through 2024 – began Thursday at 10:06 a.m. CT, Oklahoma Department of Corrections Chief of Operations Justin Farris told reporters. Cole was pronounced unconscious at 10:11 a.m. CT and pronounced dead at 10:22 a.m. CT.

Cole declined a ceremonial last meal and chose not to have a spiritual adviser with him, Farris said.

Donna Daniel, Brianna’s aunt, thanked the state for carrying out the sentence and giving justice to her late niece, whom she described as a blond-haired, blue-eyed baby.

“She died a horrific death,” Daniel told reporters, adding, “And he gets off easy and gets to get a little injection in his arm and go to sleep in his death. He did not give Brianna the chance to ever grow up, to even have her first Christmas, to meet her family.”

Asked what relatives who witnessed the execution would do now, Bryan Young, Brianna’s uncle, said, “Go back to normal.”

“As normal as it can be,” added Daniel, who also told reporters, “We should not have to wait 20 years for a 9-month-old baby to get her justice.”

Cole’s attorney called him a “person with serious mental illness whose schizophrenia and brain damage” led to him murdering his daughter, according to a statement. By the time of his death, Cole had “slipped into a world of delusion and darkness,” the attorney, Tom Hird said, and was “often unable to interact with my colleagues and me in any meaningful way.”

“Ben lacked a rational understanding of why Oklahoma took his life today,” Hird said. “As Oklahoma proceeds with its relentless march to execute one mentally ill, traumatized man after another, we should pause to ask whether this is really who we are, and who we want to be.”

Cole is the second death row inmate put to death in the series of more than two dozen executions the state of Oklahoma intends to carry out through 2024 – a spree critics have condemned amid the state’s history of botched lethal injections.

The procedure for Cole on Thursday was “uneventful and without any complications,” Farris told reporters.

His last words were a rambling, often-nonsensical stream of consciousness that referred at times to “the Lord” and “Jesus” and sometimes was too quiet to decipher, journalists who witnessed them later said.

Cole prayed for the state of Oklahoma and the United States, also stating, “I forgive everyone that I have done wrong,” recalled Sean Murphy of the Associated Press.

Both Murphy and Nolan Clay of The Oklahoman newspaper – each of whom indicated they have witnessed multiple executions – described Cole’s execution as similar to others they’d seen.

Cole’s attorneys insisted he should not be put to death because his mental condition – magnified by his exposure as a child to drugs and alcohol, substance abuse issues and physical and sexual abuse – had deteriorated so much that he was not competent to be executed, according to a clemency petition in a failed bid for mercy.

The US Supreme Court on Wednesday denied Cole’s request for a stay of execution. Cole’s attorneys also unsuccessfully asked a state appeals court to compel the inmate’s warden to refer his case for review to the district attorney to initiate a competency hearing.

Cole lived in largely ‘catatonic’ state, attorneys said

The facts of Cole’s case obligated the state to spare his life, his attorneys in recent months told parole board members, though the arguments failed. They pointed to “evolving standards of decency,” including public polling that shows disapproval for executions of the mentally ill.

Oklahoma had “the opportunity to exhibit courage, to follow these standards, and to be on the right side of history by prohibiting the execution of Benjamin Cole, a severely mentally ill and physically infirm person.”

The US Supreme Court in a 1986 ruling found the execution of the severely mentally ill to be unconstitutional, with Justice Thurgood Marshall writing, “It is no less abhorrent today than it has been for centuries to exact in penance the life of one whose mental illness prevents him from comprehending the reasons for the penalty or its implications.” And in Oklahoma, state law makes it illegal to execute someone found to be insane.

Cole, who was diagnosed with schizophrenia and had a brain lesion associated with Parkinson’s disease, lived in a largely “catatonic” state, hardly speaking to anyone, including his own lawyers, according to his clemency petition. After years of near-total isolation in the Oklahoma State Penitentiary, he used a wheelchair and existed in what one clinical psychologist described in the clemency request as his own “mental universe,” not understanding the legal proceedings surrounding his imminent execution.

“Benjamin Cole is incapacitated by his mental illness to the point of being essentially non-functional,” Hird said in a statement after an Oklahoma judge this month ruled Cole was competent to be executed.

“His own attorneys have not been able to have a meaningful interaction with him for years, and the staff who interact with him in the prison every day confirm that he cannot communicate or take care of his most basic hygiene. He simply does not have a rational understanding of why Oklahoma seeks to execute him.”

Oklahoma Attorney General John O’Connor praised the parole board’s September vote to deny clemency in a statement, noting Cole’s conviction and sentence had been upheld on appeal and rejecting questions about his mental illness.

“Although his attorneys claim Cole is mentally ill to the point of catatonia, the fact is that Cole fully cooperated with a mental evaluation in July of this year,” the attorney general said September 27. “The evaluator, who was not hired by Cole or the State, found Cole to be competent to be executed and that ‘Mr. Cole does not currently evidence any substantial, overt signs of mental illness, intellectual impairment, and/or neurocognitive impairment.’

“I am grateful that the Board denied Cole’s request for executive clemency. Our thoughts and prayers are with the other members of Brianna’s family.”

The murder of Brianna Cole

Cole was found guilty of Brianna’s brutal, December 2002 murder, per the attorney general’s office, when her cries interrupted him while playing a video game.

Cole grabbed his daughter’s ankles while she was on her stomach and forced them up to her head, breaking her spine and causing her to bleed to death, according to a probable cause affidavit. Cole then returned to his video game as his daughter died, O’Connor said.

Cole admitted in a taped confession to causing his daughter’s fatal injuries, his clemency petition said, telling police he would “regret his actions for the rest of his life.”

Before his trial, prosecutors offered him a plea deal that would have resulted in a life sentence without parole. But Cole, his mental state already deteriorating, refused to accept it – a “complete act of irrationality against self-interest,” his petition said.

Cole wanted the case to go to trial because, he told his lawyers, it was “God’s will” and “his story … would transform Rogers County, and it would allow God to touch hearts and allow Benjamin to walk away from it all a free man.”

Cole had yet to be diagnosed with schizophrenia, but his trial attorneys twice called for competency evaluations, arguing his religious delusions rendered him irrational and, as a result, he did not understand the legal proceedings. Still, he was found competent to stand trial.

Cole’s attorneys recently contended his lawyers at trial, along with the judge and bailiff, recognized the prevalence of his mental illness as the man sat in the trial “literally not moving a muscle for hours on end with a Bible opened in front of him on the table,” according to the petition. Cole did not testify and was sentenced to death.

Mental decline began decades ago, petition said

Cole’s struggles with his mental health date back to his early childhood, growing up in a junkyard surrounded by “rampant” drug and alcohol abuse, his petition said. Encouraged by the adults in his life, Cole began to drink as a young child, it said, and one of Cole’s brothers testified they would get high huffing gasoline by the time Cole was 10 years old. Cole also endured years of verbal, physical, and sexual abuse, the petition claimed.

Cole graduated high school but around that time began exhibiting “all of the marks of a person beginning to struggle with serious mental illness,” the clemency petition said, noting 18 is the typical age when early-adult onset severe mental illnesses like schizophrenia first emerge.

Cole became “isolated and withdrawn,” and a stepsister said he was depressed and didn’t have many friends, the petition said. He spent long periods unemployed, and though he joined the Air Force in 1986, he struggled with substance abuse, exhibited “impulse control problems” and was discharged the following year.

It was around this time Cole’s first wife accused him of abusing their son, and Cole was convicted and sentenced to two years in prison for aggravated child abuse, the petition said. That marriage ended, as did Cole’s second, and when he met Brianna’s mother in 1998, he was living either under a bridge or in a tent in Claremore, Oklahoma.

When their daughter was born, the petition said, Cole couldn’t keep a job and was “drinking heavily.”

Inmate’s condition warranted mercy, attorneys argued

Cole’s condition got worse in the years since his trial, years in which teams of post-conviction attorneys struggled to meaningfully communicate with him as a small parade of psychologists and psychiatrists evaluated his declining mental state, the petition states.

One diagnosed Cole with paranoid schizophrenia in 2008, finding his mental condition had deteriorated as he went untreated for almost 20 years.

That doctor also said Cole was “convinced” any discussion about his case “would undermine his faith in Jesus and undermine his current ‘saved’ status,” the petition states. Those beliefs underscore what his lawyers describe as an “implacable reticence” that interferes with their ability to work with him on his case.

His clemency petition details visits by attorneys and doctors who found Cole dirty and “unkempt” in complete darkness inside his cell, which he reportedly almost never left. Corrections officers and his case manager told Cole’s attorneys he kept the lights off at almost all times and had no regard for his personal hygiene, per the petition.

In 2015, Cole mailed his mother some of his hair and a tooth, and in 2019 he handed one of his attorneys a packet with two more of his teeth and a note the attorneys understood as a request to mail the teeth to his mother – both instances his clemency petition said exemplify his sharp decline.

Additionally, per his petition, a physician who reviewed an MRI performed on Cole this year found a lesion on his brain that “would be highly consistent” with Parkinsonism.

CNN’s Amanda Watts contributed to this report.