Kim Sung Woong, a documentary film director, listened with awe as he heard remarks by a man who was falsely accused in a high-profile murder case.

The previously condemned man's positive words were not what one would expect from a person who spent most of his life behind bars.

"It was unfortunate for me to be arrested over what I didn't commit, but it doesn't necessarily mean I have been unhappy," Shoji Sakurai told Kim seven years ago, when Kim was shooting a film about Kazuo Ishikawa, a man currently seeking exoneration from a murder case that happened over a half a century ago.

(Kimoon Film)

"I could not understand why Mr. Sakurai could say so, despite hardships unreasonably imposed on him," Kim, a second generation Korean living in Japan, said. "This curiosity inspired me to film Mr. Sakurai and other falsely accused people so I could find the answer."

His search has bore fruit as a new film "Gokutomo" (Friends in Prison), which will be shown at a Tokyo movie theater in March before its subsequent nationwide screenings.

The film features Sakurai, 71, who was jailed for almost 30 years together with Takao Sugiyama over a 1967 murder-robbery, known as the "Fukawa Incident," before their acquittal in 2011. Sugiyama died in 2015 at the age of 69.

Another lead character is Toshikazu Sugaya, 71, who was also acquitted in 2010 of the 1990 murder of a girl, the "Ashikaga Case," after serving more than 17 years of a life sentence.

The three were supporting efforts by Ishikawa, 79, who seeks a retrial over the 1963 "Sayama Case," in which a 16-year-old female high school student was killed in Sayama, Saitama Prefecture. He was convicted, based mostly on his temporary confession, and spent more than 30 years locked up before his release on parole in 1994.

All four of the men were imprisoned at the Chiba Prison, near Tokyo, and they appear to almost reminisce about their past time spent in the facility together.

"I had thought they would engage in serious conversations in talking about their experiences during the detention, but it was as if they were attending an alumni meeting," Kim said.

In the prison, they played baseball and shogi (Japanese chess) while attending singing contests.

Sakurai wrote poetry and composed songs, while Ishikawa, who was born in a severely ostracized "buraku" district, learned how to read and write while he was imprisoned though he had little schooling growing up in poverty.

"I would not be released until my innocence was proven, even if I cried and screamed," Sakurai said in the film. "So, I decided to survive by seeking out something interest."

The two also secretly exchanged information, while playing shogi, about how to achieve their exonerations through retrial.

(Kimoon Film)

Kim, who would regularly film them, said he gradually learned why they were able to remain so positive.

"For them, the prison was inevitably a place to live, to learn and to spend their youthful days," he said. "They could not help being positive, and they have affirmatively led their lives ever since their release."

In one scene in the film, Sugiyama said in jest, "I was just like a hooligan before the arrest, and I would have been murdered or would have become a gang leader if I had not been arrested."

Sakurai, for his part, indicated he has been able to meet with trustworthy people, such as lawyers and human rights activists, since he was "involved in a false accusation case not by choice as a young man who didn't think about the future at all."

Sugaya said in the film, meanwhile, "I was rather a reclusive man before the arrest and didn't intend to make friends. But I have gradually associated with others...I wonder what kind of person I would have been if I hadn't met this strange fate."

"I have found their attitudes remarkable, and I think they have gained beyond what they lost," said Kim. "Their way of living is the ultimate criticism against the judicial system that convicted them unjustly. I expect this film to make the public aware."

His previous films include "Until the Invisible Handcuffs are Removed," which focuses on Ishikawa's struggle to reopen the Sayama Case, and "Freedom Moon," depicting the daily life of Iwao Hakamada, who was convicted of a 1966 quadruple murder and released in 2014 following a 48-year detention after a district court decided to reopen the high-profile case, based on DNA tests.

The court concluded there was reason to believe that evidence had been fabricated in the original trial and that keeping Hakamada, 81, confined while awaiting retrial would have been "unbearably unjust," but he is still on death row as prosecutors appealed the lower court's decision to the Tokyo High Court.

As a death row inmate, Hakamada spent six years together with Ishikawa, who also faced the death sentence initially before a commutation to life imprisonment, at the Tokyo Detention House.

The latest film shows the friends from prison -- Ishikawa, Sakurai and Sugaya -- sometimes visit Hakamada, another "Gokutomo," at his apartment in Shizuoka Prefecture, where he lives with his elder sister Hideko.

Hideko has devotedly supported her brother, whose mental state has deteriorated due to the decades-long solitary and endless fears about execution. In an apparent reaction to being institutionalized, Hakamada began referring to himself as "the omnipotent God."

Kim said, "Mr. Hakamada must also have tried to remain positive in prison, despite the harsh conditions, and I think it has led him to create his own world, in which he himself became a 'man with power.'"

Renowned artists contributed to creating the film by providing its title tune.

Famed poet Shuntaro Tanikawa wrote the words and popular pop singer Hitoshi Komuro composed the music, while jazz saxophonist Akira Sakata, rock singer Tsuyoshi Ujiki and other famous musicians participated in the project.

"It's just like 'We are the World' in supporting those who are falsely accused," said Kim, who also plans to create the English-language version of the film so it can be screened overseas.