ST. LOUIS (AP) — A Missouri man is scheduled to be put to death Tuesday evening for sexually assaulting and strangling a 9-year-old girl whose body was thrown into a sinkhole.

Christopher Collings, 49, is set to receive a single injection of the sedative pentobarbital at 6 p.m. CST for the 2007 murder of fourth-grader Rowan Ford.

The girl was assaulted and strangled with a length of rope in the tiny southwestern Missouri town of Stella, on Nov. 3, 2007, and her body was discovered six days later in the sinkhole outside town.

Collings’ fate appeared to be sealed on Monday when the U.S. Supreme Court denied an appeal and Republican Gov. Mike Parson turned aside a clemency request. Parson, a former sheriff, has overseen 12 previous executions and never granted clemency.

Collings’ execution would be the 23rd in the U.S. this year and the fourth in Missouri — Brian Dorsey was executed on April 9, David Hosier on June 11 and Marcellus Williams on Sept. 24. Only Alabama with six and Texas with five have performed more executions in 2024.

Rowan was a fourth-grader described by teachers at Collings’ trial as a hard-working and happy student, a lover of Barbie dolls who had her room painted pink. Collings was a friend of Rowan’s stepfather, David Spears, and lived for several months in 2007 at the home Rowan shared with Spears and Rowan’s mother, Colleen Spears. The child called Collings “Uncle Chris.”

Collings told authorities that he drank heavily and smoked marijuana with Spears and another man in the hours before the attack on Rowan, according to court records. Collings said he picked up the still-sleeping child from her bed, took her to the camper where he lived, and assaulted her there.

Collings told police that he planned to take Rowan back home, leading her outside the camper facing away from him so that she couldn’t identify who assaulted her. But when moonlight lit up the darkness, Rowan was able to see him, Collings told police. He said he “freaked out,” grabbed a rope from a nearby pickup truck and killed her.

Colleen Spears returned home from work at 9 a.m. on Nov. 3 and was alarmed when she couldn’t find Rowan. Court records said Spears insisted Rowan was at a friend’s house. But when Rowan failed to return home by the afternoon, Colleen Spears called police, prompting a massive search.

Collings, Spears and a third man became the focus of police attention because they were the last people seen at Rowan’s home. Collings told police that after killing Rowan, he took the body to a sinkhole. He burned the rope used in the attack, along with the clothes he was wearing and his bloodstained mattress, prosecutors said.

Court documents and the clemency petition said Spears also implicated himself in the crimes. A transcript of Spears’ statement to police, cited in the clemency petition, said Spears told officers that Collings handed him a cord and Spears killed Rowan.

“I choke her with it. I realize she’s gone. She’s … she’s really gone,” Spears said, according to the transcript. Meanwhile, court documents said it was Spears who led authorities to the sinkhole where the body was found.

But Spears was allowed to plead to lesser charges. It wasn’t clear why. Prosecutors at the original trial didn’t respond to messages seeking comment.

Spears served more than seven years in prison before being released in 2015. No phone listing could be found for Spears.

The clemency petition said Collings suffered from a brain abnormality that created “functional deficits in awareness, judgment and deliberation, comportment, appropriate social inhibition, and emotional regulation.” It also noted that he was frequently abused and sexually abused as a child.

“The result was a damaged human being with no guidance on how to grow into a functioning adult,” the petition stated.

The clemency petition and the Supreme Court appeal both challenged the reliability of the key law enforcement witness at Collings’ trial, a police chief from a neighboring town who had four AWOL convictions while serving in the Army. Failure to disclose details about that criminal history at trial violated Collings’ right to due process, Collings’ attorney, Jeremy Weis, contended.

“His credibility was really at the heart of the entire case against Mr. Collings,” Weis said in an interview.