ST. LOUIS  • Missouri Gov. Jay Nixon said Thursday his decision to commute the death sentence of a convicted murderer was based on factors specific to the case and does not indicate a softening of his support of the death penalty.

With almost no explanation, Nixon on Monday spared the life of Richard Clay, even though the governor said he still considered Clay guilty of the 1994 murder-for-hire of Randy Martindale in Missouri's Bootheel.

At a news conference Thursday at Forest Park Community College, Nixon, a staunch death penalty advocate, said a "number of factors" contributed to his decision. Among those were the "involvement of a number of folks'' and a court system that "had some issues," with the case, he said. He offered little elaboration. He said most of the concerns about the case had been reported by the media.

"I just felt, and continue to feel, that the best decision was … not to use the ultimate penalty, but instead a very, very serious penalty and that is life without possibility of probation or parole," Nixon said.

Nixon said a shortage of the drugs used in lethal injections wasn't a factor in commuting the sentence. Nor was the role that former prosecutor Kenny Hulshof played in the case.

Clay's defense has pointed to the involvement of Hulshof in the trial as one reason the conviction might be suspect. Some other cases tried by Hulshof have been overturned on appeal, and Hulshof was found to have withheld evidence in another case where a person served 16 years in prison before being found innocent and freed. Hulshof, a Republican, was defeated by Nixon, a Democrat, in the 2008 gubernatorial election.

On the night of the murder, the defense has said, Clay, 45, was dealing drugs and, for that reason, fled from police. Questions about the involvement of two other people in Randy Martindale's murder also have dogged the case.

According to prosecutors, Randy Martindale's wife, Stacy, was involved in an extramarital affair with Charles Sanders and offered him $100,000 to kill her husband. The jury found that Sanders turned her down but that Clay, his friend, accepted. Stacy Martindale was convicted of second-degree murder and sentenced to 15 years in prison. Sanders received probation.

Throughout the appeals process, Clay's defense has claimed that Sanders had a greater motive to kill Randy Martindale than did Clay.

Nixon did not call for a board of inquiry to review the evidence in Clay's case, one option that was available to him.

"I don't think sidestepping my constitutional responsibilities is appropriate,'' he said.

Nixon noted that during his 16 years as attorney general, he was involved in 59 death penalty cases, including one argued before the U.S. Supreme Court. As governor, he oversaw the 2009 execution of death row prisoner Dennis Skillicorn.

Another execution is scheduled for next month. Nixon said he has yet to be briefed on the case of Martin Link, convicted of kidnapping, raping and murdering an 11-year-old St. Louis girl in 1991. Asked whether his commutation of Clay's sentence signaled a retreat from his support of the death penalty, Nixon said each case would be considered on its own merits.

"I have not softened my position on capital punishment,'' he said.