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 former boxer and divorcee who had also worked in a bar, the police considered him a low-life and the most likely suspect, says Tsunogae.
    On July 4, 1966, the police brought Iwao in for questioning.
    Iwao Hakamada was briefly a professional boxer who fought 29 bouts.
    At the time, many media outlets falsely reported that a blood-stained shirt found at the scene of the crime belonged to Iwao. The police let him go due to a lack of evidence and continued their investigations for a month.
    After coming to a dead end, officers circled back to interviewing Iwao and his family members. Tsunogae alleges the police were desperate for a suspect and keen to pin the crime on Iwao.
    They were taken to the police station and interrogated separately from morning till nightfall. Back at their mother's house, the family swapped notes about what they'd each been asked.
    But Iwao was kept in solitary confinement at the station with no access to legal counsel. His ordeal was just beginning.

    99% conviction rate

    Japan puts far fewer people in prison than most developed countries: 39 per 100,000 people, compared with 655 in the US and 124 in Spain, according to the World Prison Brief website.
    But in the US, for example, alleged offenders are entitled to remain silent during police questioning, have the right to legal representation both outside of and during questioning, and can make a deal to admit a less serious charge. This allows the prosecutor to drop a case and file an indictment from, for example, first degree murder to second degree murder.
    By contrast, in Japan the accused can remain silent during police questioning, but suspects can be interrogated without the presence of a lawyer.
    Iwao Hakamada and his sister Hideko (R) at their home in Hamamatsu.
    Though plea bargains were introduced in 2016, their use is limited to categories such as corporate malfeasance, according to Colin Jones, a law professor at Doshisha University, although defendants who cooperate can expect a more lenient sentence.
    The 99% conviction rate is partly because prosecutors only pursue cases they believe will lead to a guilty verdict, according to Mark Ramseyer, a law professor at Harvard University.
    "There are very few prosecutors in Japan. They are massively overworked. Given the workload, they focus first on the slam dunk, guilty-as-sin cases. They don't have time for the 'maybe he did it, maybe he didn't cases,'" says Ramseyer.
    And because crime rates are so low in Japan, if someone is arrested or prosecuted, people generally assume they have done something wrong, says Jones.
    "They only realize Japan's criminal justice system is not functioning when they are personally caught up in it," he says.

    'Hostage justice' system?

    Hideko says her brother fell victim to "hostage justice," when police allegedly strip suspects of their right to remain silent and coerce them to confess.
    Hideko claims there are no recordings that provide evidence that he confessed to mass murder. He was subject to more than 240 hours of questioning for over 20 days, according to Kiyomi Tsunogae, a member of Iwao's defense team. The police and prosecutors initially alleged Iwao had been having an affair with his boss' wife and that she had asked him to murder her family and burn their house down so they could start a new life together. But officers discarded that theory after two days, she says.
    Towards the end of the trial, they said he had wanted money.
    Police in Japan can keep suspects detained for up to 23 days and repeatedly extend this deadline by filing new accusations. CNN asked the Japanese police whether the allegations that they used forced confessions during interrogations was true, but they provided no comment.
    Confessions have long been the cornerstone of Japanese criminal justice. They are considered "the king of evidence" and "decisive element of proof" sought by every prosecutor and expected by most judges, David T. Johnson, an expert on the death penalty in Asia, wrote in a paper published in 2015.
    In most democracies, a confession obtained after more than 200 hours of interrogation would be ruled as involuntary, unreliable, and inadmissible as evidence, adds Johnson. But not so in Japan.
    In Iwao's ca