Boise, Idaho ? A man sentenced to death for the slayings of a young Texas couple camped in the Idaho wilderness must be released or retried because of his attorney’s actions, a federal appeals court ruled Tuesday.

Mark Henry Lankford has been on Idaho’s death row for more than two decades for the 1983 bludgeoning slayings of Marine Capt. Robert Bravence and his wife, Cheryl.

The Bravences were reported overdue from an extended camping trip in the summer of 1983. A week later, their van was found abandoned at a Los Angeles bus terminal, and that September hunters discovered their remains at a remote campground.

Lankford and his brother, Bryan Lankford, were arrested and each blamed the other for the crime. Prosecutors offered Bryan Lankford life in prison in exchange for his testimony against his older brother.

Mark Lankford’s attorney, Gregory FitzMaurice, told the jury they could consider Bryan Lankford’s testimony even though it was uncorroborated, the appellate court found. That prejudiced the jury against Mark Lankford and effectively denied him his right to effective counsel, the the 9th U.S. Circuit Court of Appeals found.