Iwao Hakamada was sentenced to death in 1968 after being convicted of murder and arson in connection with the killing of his boss and his boss’s family two years previously.

He was working at a miso processing plant when the owner, the owner’s wife and their two teenage children were recovered from their burnt-out home, having been stabbed to death.

He was convicted on the basis of a confession — which his lawyers said was coerced through beatings — and physical evidence which a court has now accepted was fabricated by police.

In a rare move, Mr Hakamada was freed from prison in 2014 after becoming only the fifth death row prisoner in Japan’s post-war history to be granted a retrial.

Since then, he has been living with his 91-year-old sister Hideko, who has long campaigned for his release.

Mr Hakamada did not appear in court during the retrial due to his poor mental health. A number of supporters celebrated outside the courthouse when he was formally acquitted.

It is open to prosecutors to appeal the conclusion of the retrial. A decision has not yet been announced.