A judge in the US state of Louisiana has ordered the unconditional release of Albert Woodfox who has been in solitary confinement since 18 April 1972, BBC reported.
Woodfox was in solitary confinement after a prison riot that resulted in the death of a guard at the Louisiana State Penitentiary in Angola.
Judge James Brady also banned prosecutors from trying Albert Woodfox, 68, for a third time.
Woodfox was tried twice for the guard's death, but both convictions were later overturned. He denies all the charges.
But a spokesman for the Louisiana attorney general said prosecutors would appeal "to make sure this murderer stays in prison and remains fully accountable for his actions".