HELENA — Eight years into his 100-year sentence for murder and arson, Clifford Old Horn will get a new trial because prosecutors were not clear on how they would use Old Horn’s statements he made to investigators.

In August 2011, a jury convicted Old Horn of deliberate homicide after 90 minutes of deliberation.

Prosecutors argued that Old Horn helped rob, beat and stab Harold Mitchell, 73, and a former CSKT Chairman, to death before burning down his St. Ignatius trailer on the morning of July 6, 2005.

District Court Judge C.B. McNeil sentenced Old Horn to 100 years with no possibility of parole.

Last week, the Montana Supreme Court upheld a lower court ruling granting Old Horn a new trial.

Old Horn’s attorneys argued that statements he made to investigators shouldn’t have been used against him because he believed he had immunity.

Montana Supreme Court Justices ruled that a letter from Lake County Attorney Mitch Young explaining the immunity agreement contained legal distinctions that are, “not readily apparent even to those trained in the law,” and that statements made by officers led Old Horn to believe he would not be prosecuted.

Prosecutors said without Old Horn’s statements they likely couldn’t gain a conviction.

After his conviction in 2011, Old Horn’s defense attorney, Ronald Piper, read a prepared statement expressing Old Horn’s remorse and sympathy to Mitchell’s family.

Despite the guilty verdict, Old Horn and Piper maintained that his involvement in the crime was limited.

“I have faith and trust that one day we will see the sad truth,” the statement read. “I hope the real man or woman responsible will someday hear or read my words.”

While the Lake County Attorney’s Office had asked for the maximum sentence, the defense asked for a 40-year sentence with 25 years suspended based on perceived mitigating factors.

“[Old Horn] had personally no active role killing Mr. Mitchell,” Piper said. “He did not burn the trailer. When he realized the other parties were going to beat an old man, he left. He had no active role.”

During the trial, Young said that Old Horn had told police the truth about Mitchell’s death in interviews in 2007 and 2010, which were recorded at the Great Falls Regional Prison. Young said Old Horn knew too many details — details not made public — to be innocent of the crime. Although Old Horn’s story differed from 2007 to 2010, it was because Old Horn was trying to decrease his culpability, not because he was fabricating a story, Young said.

“If there was ever a time to tell detectives what the defendant is now trying to sell you as the truth, that would have been it,” Young said about Old Horn’s 2010 interview.

McNeil referenced Old Horn’s four prior felonies and called deliberate homicide the most egregious crime in Montana law.

Cries broke out in the back of the Lake County courtroom after McNeil read the sentence.

Earlier in 2011, the state was forced to drop charges against the crime’s other three alleged co-conspirators, Nathan Ross, Nigel Ernst and Kyle Brown, after Old Horn refused to testify against them.