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.

However, the 9th U.S. Circuit Court of Appeals ruled that Lankford received ineffective assistance from his attorney, and said the state must retry him "within a reasonable time or release him."

The decision likely means a costly and protracted retrial in Idaho County, one of the state's most rural.

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 hidden at a remote campground.

The couples' skulls were so shattered that they had to be reconstructed by anthropologists, Idaho Deputy Attorney General LaMont Anderson said.

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.

Bryan Lankford testified that he engaged the campers in conversation while Mark sneaked up on them from behind. Mark Lankford ordered them to the ground, then beat them with a club, his brother said.

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 9th Circuit found.