ST. FRANCISVILLE, La. — The last inmate of a group known as the “Angola Three” pleaded no contest Friday to manslaughter in the 1972 death of a prison guard and was released after more than four decades in prison, raising a clenched fist as he walked free.

Albert Woodfox and two other men became known as the “Angola Three” for their decades-long stays in isolation at the Louisiana Penitentiary at Angola and other prisons. Their cases drew condemnation from human rights groups and focused attention on the use of solitary confinement in American prisons.

Officials said they were kept in solitary because their Black Panther Party activism would otherwise rile up inmates at the maximum-security prison farm in Angola.

Woodfox consistently maintained his innocence in the killing of guard Brent Miller. He was being held at the West Feliciana Parish Detention Center in St. Francisville, about 30 miles north of Baton Rouge. He was awaiting a third trial in Miller’s death after earlier convictions were thrown out by federal courts for reasons including racial bias in selecting a grand jury foreman.

Woodfox, who turned 69 on the same day he was released, spoke to reporters and supporters briefly outside the jail before driving off with his brother. Speaking of his future plans, he said he wanted to visit his mother’s gravesite. She died while he was in prison, and Woodfox said he was not allowed to go to the funeral.

As to whether he would have done anything differently back in 1972, Woodfox responded: “When forces are beyond your control, there’s not a lot you can do. Angola was a very horrible place at the time and everybody was just fighting to survive from day to day.”

In a news release earlier Friday, Woodfox thanked his brother and other supporters who have lobbied over the years for his release.