Oklahoma executed inmate Benjamin Cole, who was convicted of killing his 9-month-old daughter Brianna Cole 20 years ago, on Thursday despite claims from his attorneys that he had been severely mentally ill.

Cole, 57, was pronounced dead at 10:22 a.m. local time at the state penitentiary in McAlester. 

Cole murdered his infant daughter in Rogers County by forcibly bending her backward, breaking her spine and tearing her aorta. 

Attorneys did not dispute that but argued he was severely mentally ill and that he had a growing lesion on his brain that had worsened in recent years. The lesion was separate from his diagnosis of paranoid schizophrenia.

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Oklahoma Statte Penitentiary

Entrance sign and guard tower at the Oklahoma State Penitentiary (Shepard Sherbell/CORBIS SABA/Corbis via Getty Images)

Cole refused medical attention and ignored personal hygiene. He hoarded food and lived in a darkened cell with almost no communication with staff or fellow prisoners, according to his attorneys.

"His condition has continued to decline over the course of this year," Cole’s attorney, Katrina Conrad-Legler, said, noting that the lesion impacted the part of his brain that deals with problem-solving, movement and social interaction.

However, attorneys for the state and members of the victim's family told the state’s Pardon and Parole Board last month during a clemency hearing that his symptoms of mental illness were exaggerated and that the nature of the killing merited his execution.

Assistant Attorney General Tessa Henry said Cole killed his daughter because he was upset that her crying had interrupted his playing of a video game.

Prosecutors noted that the infant had numerous injuries, and that Cole had previously served time in prison in California for child abuse.

Cole was denied clemency, and a district judge determined he was competent to be executed earlier this month. 

Benjamin Robert Cole Sr.

Oklahoma executed Benjamin Robert Cole Sr. on Thursday, despite claims from his attorneys that he had been severely mentally ill. Cole was convicted of killing his infant daughter in 2002. (Oklahoma State Department of Corrections via AP, File)

Two appeals filed with the Supreme Court were rejected. 

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He was the sixth Oklahoma inmate to be executed since the state resumed executions in October 2021.

According to The Oklahoman, Cole did not request a traditional last meal and was instead given a facility "religious meal" consisting of vegetarian lasagna, salad, a tortilla and a fruit drink packet.

Oklahoma State Penitentiary in McAlester

The Oklahoma State Penitentiary in McAlester, Oklahoma, on Sept. 30, 2015. (REUTERS/Nick Oxford)

The outlet reported Cole had referred to himself as "just a super-duper hyperbolic Jesus freak" and said he hoped his spirit would return to his "Father in Heaven." 

On Wednesday, a federal appeals court panel upheld a lower court ruling that deemed the state's execution protocol constitutional. 

Cole and more than two dozen death row inmates filed suit.

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The current death penalty law was enacted in 1977 by the Oklahoma Legislature. 

The method to carry out the execution is by lethal injection.

Cole's attorneys claimed he could not be executed under a 1986 Supreme Court ruling that held the constitutional prohibition against cruel and unusual punishment prohibits states from inflicting the death penalty upon a prisoner who is mentally ill.

Fox News' Sarah Rumpf and The Associated Press contributed to this report.