By Carey Gillam

(Reuters) - Missouri on Tuesday executed a man who, along with a friend, pleaded guilty to the 1989 abduction, rape and murder of a 15-year-old girl, a state corrections department spokesman said.

Roderick Nunley, 50, was pronounced dead at 9:09 p.m. CDT after receiving a lethal injection of drugs at the state's death chamber in Bonne Terre, Missouri, corrections spokesman Mike O'Connell said.

Nunley pleaded guilty to the murder of Ann Harrison, a Kansas City high school girl who was waiting for her school bus on a March morning when he and accomplice Michael Taylor drove by and decided to kidnap and rape her, according to court papers. After assaulting her, they stabbed Harrison multiple times and left her body in the trunk of a car they had stolen.

Taylor also pleaded guilty, and was executed in April 2014.

"Despite openly admitting his guilt to the court, it has taken 25 years to get him to the execution chamber," Missouri Attorney General Chris Koster said in a statement. "Nunley's case offers a textbook example showing why society is so frustrated with a system that has become too cumbersome."

As Nunley's execution neared, his lawyers and the Missouri Attorney General's office inundated courts with claims and counterclaims over whether the execution should proceed.

In an appeal to the U.S. Supreme Court, lawyers for Nunley argued among other things that the death penalty constitutes "cruel and unusual punishment."

The Supreme Court turned down multiple requests for a stay, the last on Tuesday arguing that Nunley's attorney had conflicts of interest and should have been removed.

Janel Harrison, the victim's mother, said before the execution she and her husband, Bob Harrison, were looking forward to gaining some closure.

"For the past 26 years there have been times when Bob and I have felt compassion for Nunley, Taylor and their families only to remember how frightened Ann must have been," she said.

"The total fear she felt when she was bound and unable to defend herself while listening to them discuss how they were going to kill her. The pain she felt when they stabbed her, not once, but at least 10 times. That is the true definition of unusual pain and suffering. The only closure that our family will have is knowing that justice for Ann has been attained and that we are finally through with the judicial system."

(Reporting by Carey Gillam in Kansas City, Missouri; Editing by Mohammad Zargham and Sandra Maler)