Ahn Yong-soo no longer has many pictures of his older brother, Ahn Hak-soo. Decades ago, they were seized by the South Korean government and never returned to his family. Ahn keeps the few remaining black and white photographs closely guarded in an album. One image, shot in 1966 is the last known picture ever taken of Hak-soo.

"This was in Saigon, when he was working in a South Korean army medical unit during the Vietnam War," Ahn 60 says. "It was taken just a couple months before he went missing."

Like tens of thousands of other South Korean soldiers, Ahn Hak-soo, then 23 years old, served alongside South Vietnamese and American forces during this Cold War era conflict. But Communist North Vietnam also had an ideological ally at its side: North Korea.

Little is known about his journey, but Ahn Hak-soo did eventually make it back to the Korean Peninsula, just to the wrong side of the demilitarized zone. Ahn Yong-soo says he and his family had no idea what had happened to his brother until March 1967 when they overheard Hak-soo speaking on a radio announcement, broadcast out of Pyongyang.

"He was saying things like South Korea is a puppet of the United States, and that he was starving while in Vietnam. He gave the names of my father, my other brothers and me," Ahn recalls. "His voice sounded strained, like he was reading from a paper."

To the ears of his family, it was obvious that Hak-soo had been taken across enemy lines and brought back to North Korea. However, the South Korean government, then a military dictatorship, thought differently. Ahn says Seoul accused his brother of the worst crime imaginable at the time: defection.

Targetted for 'special attention'

His entire family was deemed guilty by association.

"My father lost his job as headmaster of a school and was forced to work in a factory. My younger brother and I were denied entry to university, and I was called in by the government's security agency to give reports on what my family was doing," Ahn says.

It was during these interrogations, up to three times a month, that Ahn says he was tortured at the hands of his own government. He claims he was hung upside-down and beaten with a shovel, that guns and knives were held to his head, that he was dipped face first into water that had been mixed with pepper.

But what Ahn says still gives him nightmares were the times the agents placed a bucket over his head so he'd be unable to see when or where their punches and kicks would strike his body next.

South Korean human rights groups say Ahn's story is not unusual. Many families whose loved ones had gone missing were treated like traitors themselves. It's a dark side of the nation's history that has only recently come to light.

Ahn says the beatings did stop after several years, but his family remained in suspicion for the next two decades. Even when Ahn took up theology studies at a university in Scotland in the mid-1980s, the South Korean embassy kept close tabs on his whereabouts, he says.

"They were making me go crazy," Ahn says. "I was so filled with anger, I wanted to kill them. The stress caused me to loose my vision. I had to return back home for medical treatment. I ended up spending five months in a psychiatric hospital."

Lack of evidence

Ahn's quest to clear his brother's name and seek justice for his family began in 2001 at the side of his father's deathbed.

"It was his dying wish: He wanted me to find out the truth about Hak-soo," Ahn says.

Ahn made repeated requests to Seoul's defense ministry to re-open his brother's case. He was told that unless evidence could be given to show that Hak-soo had indeed been kidnapped and brought to the North against his will, nothing could be done.

He was close to giving up, when, in 2008, a journalist familiar with his situation handed him government documents that detailed formerly classified information about South Korea's involvement in the Vietnam War.

"The papers showed that my brother had been listed as a prisoner of war shortly after his disappearance, and that it was believed he was taken to North Korea by force," Ahn says as he flips through the pages of a binder filled with documents related to his brother. "The government covered it up, they knew all along he wasn't a traitor."

As more information came into his hands, Ahn succeeded in persuading the defense ministry to recognize Hak-soo as a prisoner of war and not a deserter.

Last year, the nation's top court awarded Ahn and his family around $220,000 (165,000 euros) in compensation for the years of abuse they endured. It was a fraction of what he had asked for.

But even though Ahn has set his brother's record straight, he says he feels that his family's reputation still hasn't been fully repaired.

"Until the government admits and apologizes for covering up my brother's abduction, then our honor is only partially restored."