A Japanese man who spent almost half a century on death row has been found not guilty of multiple murders, in a closely watched trial that has raised questions about Japan’s use of the death penalty.

Iwao Hakamada, now 88, was sentenced to hang in 1968 after being found guilty of murdering his boss, his wife and their two teenage children, and setting fire to their home two years earlier.

The former professional boxer spent 46 years on death row – believed to be the longest time spent on death row of any prisoner worldwide – until he was freed in 2014 when new evidence emerged and a retrial was ordered.

Hakamada has consistently protested his innocence and said investigators forced him to confess, while his lawyers alleged police had fabricated evidence.

There was no immediate decision on whether prosecutors will appeal against the verdict, which was reported by Kyodo news agency and other Japanese media outlets. His defence lawyers have urged prosecutors not to challenge the ruling.

His 91-year-old sister, Hideko, who has campaigned tirelessly on behalf of her brother, told reporters ahead of Thursday’s verdict: “For so long, we have fought a battle that has felt endless. “But this time, I believe it will be settled.”

Prosecutors had again demanded the death penalty, but legal experts had suggested he would be acquitted, pointing to four other retrials involving death row inmates in postwar Japan that all saw their convictions overturned.

Hakamada, whose physical and mental health deteriorated during his long incarceration, was not present at Thursday’s ruling and has been represented by his sister during the retrial.

The outcome rested on the reliability of bloodstained clothes that prosecutors said Hakamada had been wearing at the time of the murder, at a miso factory in central Japan where he was a live-in employee.

When it ordered a retrial in March 2023 after years of legal wrangling, the Tokyo high court said there was a strong possibility that the clothing had been planted in a tank of miso by investigators. Defence lawyers said DNA tests on the clothes proved the blood was not Hakamada’s.

The high court had initially decided not to reopen Hakamada’s case – a cause célèbre for opponents of capital punishment – but reversed its decision after the supreme court ordered it to reconsider in 2020.

Hundreds of people had queued outside in the Shizuoka district court on Thursday in the hope of securing a seat in the public gallery, while supporters held up banners demanding Hakamada’s acquittal.

Hakamada initially denied robbing and fatally stabbing the victims, but confessed after what he later described as a brutal police interrogation that included physical abuse.

Campaigners said his ordeal had exposed flaws in Japan’s criminal justice system and the cruelty of capital punishment.

Death row inmates in Japan – one of only two G7 countries along with the US that retains the death penalty – are notified of their execution, by hanging, just a few hours in advance and given no opportunity to speak to their lawyers or families. Their final conversation is usually with a Buddhist priest.

But the death penalty has high levels of public support. A 2019 poll by the Japanese government found that 80% of respondents viewed capital punishment as “unavoidable”, while just 9% supported abolition.

Hakamada’s case is “just one of countless examples of Japan’s so-called ‘hostage justice’ system”, said Teppei Kasai, Asia programme officer for Human Rights Watch. “Suspects are forced to confess through long and arbitrary periods of detention” and there is often “intimidation during interrogations”.

With Agence France-Presse