Woo Yong Gak will be among 1,500 prisoners freed on Thursday to mark the first anniversary of the inauguration of the South Korean President, Kim Dae Jung. More than 7,000 others will receive pardons and the restoration of their civil rights.
"The amnesty was granted to create harmony among the Korean people and give an opportunity to everyone to participate in an effort to help the economy recover," said South Korea's Justice Minister, Park Sang Cheon, when making the announcement.
Woo, 71, was a North Korean soldier when he was captured in a military boat off the east coast of the peninsula in July 1958, at the height of the Korean Cold War.
He was sentenced to life imprisonment for spying. He might have expected parole after 18 years but he belonged to a group of political prisoners known as "the unconverted", who refused to renounce Communism. The six men arrested with him have died or been released, but since his late twenties Woo has been kept in isolation.
He says that after his arrest he was tortured, first by being held in a freezing underground chamber, later with electric shocks. He has had few visitors during his four decades in prison, but religious leaders and human-rights activists who have met him say he suffers from facial paralysis and speech impairment as the result of a stroke.
Like the 17 other long-term prisoners who will also be released on Thursday, Woo could have gained his liberty a year ago when the newly elected President Kim, a former democracy activist who was himself imprisoned for political crimes by South Korea's former military dictators, announced his first amnesty.
But even then there was a condition: to claim amnesty, prisoners had to sign a document promising to obey South Korean laws, including, by implication, the country's anti-Communist legislation. The condition, intended to placate South Korean conservatives, disappointed many of President Kim's own supporters. Woo and the 17 others refused to sign, and yesterday were granted unconditional amnesty.
North Koreans captured by the South sometimes refuse to co-operate because they fear that their families in the North will be persecuted. "It's inhumane to insist that they sign the oath, because we know that will put their families in danger," Mr Park said.
The fate of the men after their release is uncertain, but Mr Park indicated that they might be returned to North Korea in return for 300 elderly South Koreans captured during the 1950-53 Korean War.
"We cannot reveal the plans at present," he said. The Minkahyup human- rights organisation welcomed the announcement but said it came "too late [for] long-term prisoners who are mostly sick from confinement and torture".
"There are some 200 prisoners of conscience still in jail," the group said in a statement. "Kim Dae Jung's government should release all prisoners of conscience."