Albert Woodfox, who was the last inmate of a group known as the 'Angola Three' and spent a record 43 years in solitary confinement was freed from a US prison after more than four decades in prison.
Woodfox, who was kept in solitary following the 1972 murder of a prison guard, Brent Miller for which he has always maintained his innocence, marked his 69th birthday on when he was released.
A former Black Panther activist, Woodfox twice managed to overturn his conviction for the crime, but Louisiana's attorney general had been determined to pursue a third trial and managed to bar Woodfox's release on appeal.
"Although I was looking forward to proving my innocence at a new trial, concerns about my health and my age have caused me to resolve this case now and obtain my release with this no-contest plea to lesser charges," Woodfox said in a statement.
"I hope the events of today will bring closure to many."
The plea is not an admission of guilt but instead a legal maneuver in which he "does not contest that the State would present evidence at a new trial from witnesses who said he committed this crime," his lawyers said.
Meanwhile, Barack Obama used his executive powers to ban solitary confinement for juveniles in all federal prisons. He has also commissioned a review into the use of solitary confinement in the US.
"If our ultimate goal of our criminal justice system is to give people a second chance, after they've paid their debt to society, we're basically setting them up to fail if we don't take seriously the long-term negative consequences of prolonged solitary confinement," President Barack Obama's spokesman Josh Earnest told reporters.
"The kind of reforms that the president put forward are the kind of reforms that can only be implemented in the federal prison system," he said.
His two fellow Angola Three allies were already freed. Robert King, who spent 29 years in solitary was released after having his separate conviction overturned, Herman Wallace was released in 2013 and died shortly after of cancer.
Yet many of the 80,000 people estimated to be in solitary confinement in US prisons have been there for years on end.
"Today should also mark a pivotal new chapter in reforming the use of prolonged solitary confinement in US prisons and jails," said Jasmine Heiss, a campaigner with Amnesty International USA.
"Moving forward, Woodfox's case must serve as a tragic reminder of the cruelty inflicted by the prison system at its most extreme."