When Albert Woodfox, the longest-standing solitary confinement prisoner in the US who has been in isolation almost without pause for more than 42 years, was told on Thursday his conviction had been overturned, he had difficulty reading the court ruling. Prison guards refused to unshackle him, to free his hands.

“The guards wouldn’t release even one shackle from his hand so that he could turn the pages. I had to turn them for him,” said his lawyer, Carine Williams.

The 37-page ruling from the US court of appeals for the fifth circuit gives Woodfox, 67, the only member of the “Angola Three” still imprisoned, his greatest hope yet of release. He has been held in a 6x8ft cell, enduring the psychological impact of isolation exacerbated by chronic claustrophobia, for all but three years since he was put in “closed cell restriction” in 1972.

Woodfox was convicted of the murder that year of a guard in Angola prison, in Louisiana, where he was serving time for armed robbery. He has always protested his innocence, insisting that he and his Angola Three fellows were victims of a political vendetta because of their then membership in the Black Panther party.

The fifth circuit judges upheld a lower court’s opinion that Woodfox’s conviction was secured through racially discriminatory means. In 1993 he was reindicted for the murder of prison guard Brent Miller – after an earlier court ruling had overturned the sentence – by a grand jury led by a white foreperson.

The court found unanimously that the selection of the foreperson formed part of a discriminatory pattern in that part of Louisiana. Concluding that it amounted to a violation of the US constitution, the judges struck down Woodfox’s conviction.

Williams, an attorney with the New York firm Squire Patton Boggs, said Woodfox was numb when she told him his conviction had been overturned. “He was shocked. He’s been so close before, only to have it taken away from him.”

The prisoner said he wished he could have shared the news with Herman Wallace, another member of the Angola Three. Wallace was released in October 2013, when in the terminal stages of liver cancer and at the end of a bitter struggle with the Louisiana authorities. He died two days later.

In the course of almost 43 years in solitary confinement, Woodfox has only had one period, of about three years, among the general prison population. The rest of the time he has been alone, spending 23 hours a day in his cell and one hour, also in isolation, in a concrete exercise yard.

The ordeal of prolonged solitary confinement, which has been likened by international bodies to a form of torture, is amplified in his case by his claustrophobia. Legal documents give clues to the intensity of his torment.

In one such document, from 2008, he describes an attack of claustrophobia: “I feel like I am being smothered, it is very difficult to breathe, and I sweat profusely. It seems like the cell walls close in and are just inches from my face. I try to cope by pacing, or by closing my eyes and rocking myself.”

The appeal court ruling is not the end of Woodfox’s travails. He must now wait to hear what the state of Louisiana intends to do – whether it will follow the tough approach it has taken for the past 42 years and subject him to a third trial for the 1972 murder, or whether it will admit defeat and release him.

“Louisiana has fought hard, and they have lost at every turn,” said Williams. “I am hoping that they are sobered by this unanimous court decision and instead of being aggressive and going forward with a retrial they will stop and reflect on what they have done.”

Robert King, the third member of the Angola Three, was released in 2001 after 29 years in solitary. He told the Guardian “this is what we have been waiting for, for so long”, and added: “We’re now back at the point where it’s in the hands of the state.”

Tory Pegram, of the campaigning group the International Coalition to Free the Angola 3, said: “We strongly believe this is an opportunity for the state of Louisiana to stop wasting taxpayer money and do the right thing by this man who has experienced the very worst, most horrific and broken parts of the criminal justice system in America.”

