BOISE -- In a 4-1 decision, the Idaho Supreme Court vacated 60-year-old Mark Lankford's murder conviction and sent the case back to district court for a new trial.

Lankford was originally sentenced to death by an Idaho County judge in 1984 for the beating deaths of Texas Marine Captain Robert Bravence and his wife Cheryl at a remote campsite outside of Grangeville.

Mark's brother, Bryan Lankford, was also convicted. Both brothers have blamed the other for the crime.

Lankford appealed his conviction, and his case was eventually overturned by the 9th U.S. Circuit Court of Appeals. He was retried in 2008 and again found guilty of both murders.

The district court sentenced Lankford to two consecutive fixed life sentences. Again, Lankford appealed.

The Idaho Supreme Court opinion states that prosecutors failed to disclose additional promises made to a key state witness before Lankford's second trial.

The ruling says that before the trial a prosecutor told witness Lane Thomas, who was an inmate in the state correctional system, that he would try to help him "get out of the prison system" and placed on probation ahead of his testimony. A prosecutor also told the witness that he would contact the Latah County Prosecutor's Office to try and get him released. Those promises were never disclosed to the defense.

The opinion issued Monday also states prosecutors failed to correct false testimony provided by Thomas at trial.

The Idaho Supreme Court found Lankford's constitutional rights to a fair trial were violated and vacated his conviction.

It's unclear when or where a new trial will take place.

The Idaho Attorney General's Office is still reviewing the decision and had no comment on Monday.