BONNE TERRE, Mo. -- Corrections officials on Tuesday were preparing for Missouri's first execution in nearly four years, even as attorneys for Dennis Skillicorn continued efforts to spare his life.

Skillicorn, 49, was scheduled to die by injection at 12:01 a.m. Wednesday at the prison in Bonne Terre.

Skillicorn was among three men convicted of killing Excelsior Springs businessman Richard Drummond in 1994, who had stopped to help the men after their car broke down on Interstate 70.

Gov. Jay Nixon on Tuesday denied a clemency request for Skillicorn, noting that Skillicorn was on parole for another murder at the time Drummond was kidnapped, robbed and killed. Nixon also noted that Skillicorn was convicted of two subsequent murders in Arizona.

Shortly after Nixon announced his decision, the Missouri Supreme Court said it had rejected a fifth motion by Skillicorn's attorneys seeking to delay the execution. Tuesday night, the U.S. Supreme Court denied four applications for a stay.

Skillicorn on Tuesday declined an interview request.

Supporters wanted Skillicorn's sentence commuted to life in prison, calling him a role model for other inmates. Skillicorn is chairman of the hospice program at the Potosi Correctional Center, the prison where death row inmates are housed before being moved to Bonne Terre for execution. He co-founded a program that teaches inmates to be better parents. He compiled a book aimed at persuading juvenile offenders to turn their lives around.

"We need him out there," Sam Finley, a volunteer at Potosi, said. "We've got some bad eggs and they can destroy the whole complex. You need some positive role models."

Skillicorn's attorney, Jennifer Merrigan, had sought a stay of execution on several grounds. One questioned whether Nixon, the state's longtime attorney general, could fairly decide clemency when he previously worked against Skillicorn. Another cited ongoing concerns about Missouri's three-drug execution method. Those concerns are what had put executions in the state on hold since October 2005, when convicted killer Marlin Gray was put to death.

Several other states have wrestled with the same issue. Last year, the U.S. Supreme Court upheld lethal injection. And in July, a federal judge ruled that Missouri's execution method was constitutional.

Skillicorn grew up in Kansas City. In an interview last year with The Associated Press, he said that by age 13 he was injecting himself with drugs. He dropped out of high school, entered a reformatory for burglary, and started looking to older criminals as role models.

In 1979, Skillicorn and two other men killed Wendell Howell, 81, during a home invasion near Levasy in rural Jackson County. Skillicorn was convicted of second-degree murder.

He got out of prison in 1992, and two years later met Allen Nicklasson at a drug rehab center in Kansas City. The men, along with then-17-year-old Tim DeGraffenreid, decided to go on a drug run to St. Louis.

When their car broke down outside Kingdom City, Drummond stopped to help. The men forced him at gunpoint to drive then toward Kansas City. But once in Lafayette County, Nicklasson ordered Drummond to pull off on a rural road and get out.

Nicklasson told AP that Skillicorn had nothing to do with the killing. He said he left Skillicorn and DeGraffenreid behind and walked Drummond toward a field, where he shot him twice in the back of the head.

But former Lafayette County prosecutor Page Bellamy said it was Skillicorn who took the wallet out of Drummond's pants, then told DeGraffenreid to tell Nicklasson to "empty the clip in his head."

The men stole Drummond's Dodge Intrepid and drove to Arizona. When the vehicle broke down in the desert, they approached the home of Joseph Babcock, who was shot and killed by Nicklasson after driving the pair back to their vehicle. The victim's wife, Charlene Babcock, was then killed at the couple's home.

Skillicorn pleaded guilty and received two life sentences in the Arizona killings.

Nicklasson is also on death row in Missouri. DeGraffenreid pleaded guilty to second-degree murder and was sent to an undisclosed prison.

Members of a group called Missourians To Abolish The Death Penalty stood with signs near the J.C. Nichols fountain on the Country Club Plaza on Tuesday evening to protest Skillicorn's execution. They said they were disappointed that their protest didn't help in this case, but still hope their voices will be heard.