A recent decision by the Supreme Court to grant a retrial to an 85-year-old man who did time for a 1985 murder in Kumamoto Prefecture marks yet another case for establishing clear rules on the disclosure of evidence possessed by investigation authorities. In recent years, there have been several retrials and subsequent acquittals of people convicted of murders based on evidence presented to courts for the first time in the process of seeking a retrial. However, there is currently no legal provision requiring prosecutors to submit all the evidence they hold when attorneys for convicted people seeking a retrial call for disclosure, and the matter is often left to the discretion of the judge handling each particular case. Legal clarity on the matter is long overdue.

Koki Miyata was sentenced to 13 years in prison for the murder of a man in what is now the city of Uki, Kumamoto Prefecture, in 1985 — a decision that was finalized by the Supreme Court in 1990. Miyata confessed to the crime during the police investigation but pleaded not guilty throughout the court proceedings. He was provisionally released in 1999 after spending time behind bars, and a retrial plea filed by his lawyer, who also served as his guardian since Miyata began suffering from senile dementia, was accepted by the Kumamoto District Court in 2016 and endorsed by the Supreme Court earlier this month.

In the absence of hard evidence linking him to the murder, Miyata's confession held the key to his guilty verdict. But during the proceedings for seeking the retrial, pieces of cloth found by his lawyers among the evidence that prosecutors had held cast serious doubts over the credibility of his confession — that he had burned the cloth after using it to wrap around his murder weapon.