Tim Franks looks at the case of two US inmates who have been held in solitary confinement in Louisiana for what will be 40 years this month.
It's believed to be the longest period of time in US penal history.
For most of their confinement Albert Woodfox and Herman Wallace were held in the Louisiana State Penitentiary, a prison often known as "Angola", after the origin of the people who worked there when it was a slave plantation.
The two were originally imprisoned for armed robbery.
The men who later became known as the Angola 2 were linked to the Black Panther party, and fought for better prison conditions for the black inmates, and an end to the widespread rape and harsh work conditions.
While in prison there, they were charged with the murder of a prison guard, and convicted on the evidence of a prison inmate who had been promised his freedom if he testified against them.
For most of the time since then they have been held in solitary confinement.
The official reason has remained the same for 40 years: fear that the men would re-start their Black Panther-type activism and organise younger inmates as militants.
The use of solitary confinement is on the increase in the US - we ask are there good reasons for its use, and whether it is compatible with US and international law.