This Japanese man spent almost five decades on death row. He could go back

Iwao Hakamada looks out the window of his home in Hamamatsu in Japan's Shizuoka prefecture.

Hamamatsu (CNN)Sitting in an armchair next to his sister, in a cozy living room in the Japanese city of Hamamatsu, Iwao Hakamada looks like your average 83-year-old grandpa.

But in 2014, he became the world's longest-serving death row inmate, after spending nearly five decades in a tiny, solitary cell waiting for the hangman's call.
    In 1966, the former professional boxer-turned-factory worker was accused of robbery, arson and the murder of his boss, his boss' wife and their two children. The family was found stabbed to death in their incinerated home in Shizuoka, central Japan.
      Iwao initially admitted to all charges before changing his plea at trial. He was sentenced to death in a 2-1 decision by judges, despite repeatedly alleging that police had fabricated evidence and forced him to confess by beating and threatening him. The one dissenting judge stepped down from the bar six months later, demoralized by his inability to stop the sentencing.
      A pair of blood-spattered, black trousers and his confession were the evidence against Iwao. The alleged motive ranged from a murder by request to theft.
      But in 2004, a DNA test revealed that blood on the clothing matched neither Iwao nor the victims' blood type.
        In 2014, the Shizuoka District Court ordered a retrial and freed Iwao as he awaited his day in court, on the grounds of his age and fragile mental state. But four years later, the Tokyo High Court scrapped the request for a retrial, for reasons it would not confirm to CNN.
        That means Iwao could go back to prison and face the death penalty -- again.
        His legal team has launched an appeal to get a retrial and is waiting to hear from the Supreme Court.
        But in Japan, where the criminal justice system has a 99.9% conviction rate, clearing his name will not be easy.

        Unexpected arrest

        The youngest of six siblings, Iwao grew up in the seaside city of Hamamatsu, around two hours from Tokyo by train.
        The family was poor but enjoyed a happy and stable environment, says Hideko Hakamada, Iwao's 86-year-old sister, who has campaigned to clear his name. Iwao now suffers from mental illness brought on by decades of imprisonment.
        As children, the siblings went fishing by the seaside during summer and roasted garlic cloves amongst the fallen leaves in their yard in autumn. Only three years apart in age, Hideko and her little brother -- who she describes as calm and quiet -- were close. "He was like my shadow. He would follow me around everywhere," Hideko remembers.
        Photos of Iwao Hakamada spread along the tatami mat at his home in Hamamatsu.
        As the pair grew up, Hideko got married and Iwao started working in a bodybuilding gym. A colleague encouraged him to take up boxing.
        In 1959, at the age of 23, he started his professional career as a featherweight boxer and went on to fight 29 bouts. After his conviction, he was dubbed the "Japanese Rubin Carter" by some Western media. Carter was an American-Canadian boxer who was wrongfully convicted of murder but freed after serving almost 20 years in prison.
        In 1961, Iwao retired after he fell ill and got a job as a factory worker at a soybean processing plant in Shizuoka. At the time, he was divorced and had a son.
        On June 30, 1966, the news broke that Iwao's boss and family had been murdered in the early hours of the morning.
        From the start, the odds were stacked against Iwao. As a form