Updated

The U.S. Supreme Court is considering final appeals from a man scheduled to be executed Tuesday in Missouri for the kidnapping, rape and stabbing death of a 15-year-old girl more than two decades ago.

Roderick Nunley, 50, is scheduled for lethal injection at 6 p.m. CDT. Investigators say he and his co-defendant randomly targeted and kidnapped Ann Harrison as she waited outside her Kansas City home for the school bus in 1989. The girl was then raped and fatally stabbed.

If the court doesn't step in, Nunley would be the sixth death-row inmate to be executed this year in Missouri. Nunley's co-defendant in the case, Michael Taylor, was executed last year.

Nunley's attorney has three appeals before the U.S. Supreme Court, including one that says the death penalty amounts to cruel and unusual punishment — an argument rebuffed by a detective who helped break the case.

Retired Kansas City detective Pete Edlund said the only thing cruel and unusual is how long Nunley and Taylor remained on death row. He said Nunley should have been put to death long ago.

"They just take forever to do the deed," Edlund told The Associated Press in an interview this week. "The delay in executing these two is just nuts because it didn't have anything to do with their guilt. It was legal mumbo jumbo nonsense."

The other two pending appeals take issue with Missouri's process of secretly acquiring its execution drug and argue that Nunley should have been sentenced by a jury, not a judge.

Death penalty opponents also have filed a clemency petition with Gov. Jay Nixon. It alleges that racial bias played a role in the case because a prosecutor refused a plea deal that would have given Nunley life in prison without parole. Nunley is black, as was Taylor, while the victim was white.

According to prosecutors, Nunley and Taylor binged on cocaine and stole a car in the pre-dawn hours of March 22, 1989. At one point, a police officer from neighboring Lee's Summit chased the car but was called off by a supervisor when the stolen car crossed into Kansas City.

Later that morning, the men were driving around Kansas City when they saw Ann standing on her driveway, waiting for a school bus. Taylor and Nunley quickly grabbed the 15-year-old girl and took her to Nunley's mother's home. She was raped and sodomized, then stabbed repeatedly in the stomach and neck.

Taylor and Nunley put the girl's body in the trunk of the stolen car, then abandoned it in a residential area. The body was found three days later.

Edlund said the case was cracked months later when a man in jail for robbery — and seeking a $10,000 reward in the case — turned in Taylor and Nunley. Both men confessed, and some of Ann's hair was found in carpeting at the home where the crime occurred.

Edlund said the killing was haunting. He noted that her father was a former reserve officer with the police department, and her uncle was a Kansas City officer.

"To all of us, she was part of our police family," Edlund said. "That made it even more important that we solve the case."