A US man has been executed for killing a good Samaritan who stopped to help him and his friends after their car stalled in 1994.
Allen Nicklasson, 41, was pronounced dead eight minutes after the process began, in Missouri's second execution in three weeks.
His eyes remained closed throughout and he showed little reaction to the drug, only briefly breathing heavily about two minutes into the process. He offered no final words.
Missouri Department of Public Safety spokesman Mike O'Connell said Nicklasson prayed briefly with the prison chaplain about 20 minutes before the execution. No one from his family or the victim's family attended.
An appeals court panel had granted a stay of execution for Nicklasson on Monday, citing concerns about his counsel at trial and sentencing in 1996. That stay was taken up to the US Supreme Court, which did not return its 5-4 decision to end the stay until late on Wednesday night.
Missouri governor Jay Nixon refused to grant clemency and Nicklasson was executed nearly 23 hours after he was originally scheduled to die.
Nicklasson declined interview requests this week, but in a 2009 interview he spoke of a childhood scarred by abuse and mental illness. He recalled watching his mother using heroin. She also fed him dog food for dinner, he said, and once made him fight a Doberman for money.
Nicklasson was often removed from home and spent part of his childhood in mental institutions and homes for boys. He became addicted to drugs.
He met convicted killer Dennis Skillicorn in 1994 at a drug rehab centre in Kansas City. The men, along with Tim DeGraffenreid, drove to St Louis to buy drugs in August that year. On the way back, their car broke down. They dropped the car off with a mechanic and burgled a home, stealing money and drugs.
The next day, despite mechanics' warnings that the car would not last, they got back on Interstate 70 where it broke down again.
Richard Drummond, 47, who was a technical support supervisor for the AT&T telecoms company, spotted the stranded motorists and stopped to help. The men put a gun to his head and ordered him to drive his own car west.
About 60 miles later the men ordered Mr Drummond off the road to a secluded area. Nicklasson recalled that he left Skillicorn and DeGraffenreid behind and walked Mr Drummond to a field.
Nicklasson said he had intended to tie him up to buy time for the trio to get away. Instead, he ordered Mr Drummond to kneel and cross his legs, then shot him twice in the head. Mr Drummond's remains were found eight days later.
"I'm laughing, pacing," Nicklasson said, recalling the moment. "I started losing it. I wouldn't want this out, but I felt a euphoria. I finally got back for all the beatings I took" as a child.
Nicklasson and Skillicorn drove Mr Drummond's car to Arizona, where it broke down in the desert. They approached the home of Joseph and Charlene Babcock, and Nicklasson killed Mr Babcock after the man drove them back to their vehicle. Ms Babcock was killed at the couple's home.
Nicklasson and Skillicorn were sentenced to life in prison for the Arizona killings and also sentenced to death in Missouri for Mr Drummond's death. Skillicorn was executed in 2009.
DeGraffenreid pleaded guilty to second-degree murder and did not receive a death sentence.
Nicklasson's execution was the state's second to use a single drug, pentobarbital.