Montana's parole board rejected a clemency application from Barry Beach, meaning he will continue serving his prison sentence for a 1979 murder.
The Montana Board of Pardons and Parole announced Wednesday it was denying Beach's fourth clemency application since 1994.
The Poplar man is serving a 100-year sentence for the beating death of high-school classmate Kim Nees.
He was released for 18 months after a judge ordered a new trial, but the Montana Supreme Court sent him back to prison last year.
The parole board accepts clemency applications if an inmate can prove a substantial change of circumstances has occurred in his case.
"Is there significant change from the last application in 2007 until today to warrant moving it forward? ... We have unanimously concluded there is not," said Chair Mike McKee.
Wednesday, Beach said he and his legal team are already looking into other options, including pursuing cases in state or federal court.
"It's going to be a long road from here forward, but it's not over," he said.
He said he will use the strength of his supporters to stay motivated and optimistic. "They all keep reminding me. They say, 'We will not quit. We will not quit until you're free.'"