The morning of April 17, 1972, Mr. Woodfox said, he was on his way back from picking up some papers from an inmate paralegal when rumors began spreading that a white corrections officer had been murdered. Guards pulled Mr. Woodfox and other inmates into a room where they were strip-searched. After a night in a solitary cell called “the dungeon,” Mr. Woodfox and a fellow Black Panther, Herman Wallace, were charged with murder and sent to the one-man cells where they would spend the next four decades.

The officer who had been killed was Brent Miller, a former standout high school wide receiver who had just turned 23. At the time, his father also worked at Angola, overseeing the crops and livestock and his brother was a corrections officer at the prison. Brent Miller knew the prison was overcrowded, understaffed and dangerous — another officer had been set on fire the day before. When Brent Miller was found on the morning of the 17th, he had been stabbed 32 times.

“Do I believe he did it?” Stan A. Miller, another of Brent Miller’s brothers who at one time worked at the prison, too, said when asked about Mr. Woodfox. “Hell yeah, I believe he did it.” Mr. Miller said an eyewitness told him as much in 1995.

Still, that witness, Leonard Turner, testified in 1998 that he had not seen the murder and then in 2002 signed a statement for Mr. Woodfox’s lawyers saying that he did see the murder but that he knew “for an absolute fact” that Mr. Woodfox had not been involved.

Mr. Turner’s is only one of the problematic witness accounts on which the case rested; no forensic evidence was found that tied Mr. Woodfox or Mr. Wallace to the murder. Mr. Woodfox’s lawyers highlighted not only the inconsistency of the accounts but also incentives that in some cases were undisclosed by prosecutors before trial: an unusual furlough for one witness, a governor’s pardon for another and for one, a transfer to a custody situation with such minimal security that he was able to rob three banks while still under state supervision.

Mr. Miller’s widow eventually came to doubt the guilt of Mr. Woodfox and Mr. Wallace, creating something of a break with her former in-laws, who remain convinced that he did it.

At a 1973 trial, Mr. Woodfox was convicted. Mr. Wallace was convicted the next year. And so they sat, alone.