The acquittal of a 85-year-old man last month in the retrial of a 1985 murder in Kumamoto Prefecture is the latest in a series of court rulings in recent years that have reopened cases or reversed convictions of people accused of murder based mainly on their confessions in the absence of hard evidence linking them to the crime. To prevent more false charges or convictions, the parties involved in criminal investigations and the judiciary need to identify what can be learned from the process that led to a guilty ruling on Koki Miyata — who waited 34 years before he was acquitted.

Miyata was arrested over the January 1985 murder of a 59-year-old acquaintance at the victim's home in what then was the town of Matsubase in Kumamoto. He started to plead not guilty halfway through the district court trial, which nonetheless sentenced him to 13 years in prison, judging that his earlier confession to investigators was credible enough. The ruling was finalized by the Supreme Court in 1990 and Miyata was given a provisional release in 1999. Since Miyata suffered from senile dementia, his guardian filed a retrial plea in 2012, which was granted four years later. Now bedridden in a nursing home in Kumamoto, Miyata was officially acquitted in the retrial that quickly wrapped up last month.

The key that reopened his case and acquitted him in the retrial was a piece of evidence that his defense team found in the possession of prosecutors — but had never been submitted to the court in his initial trial. It was a part of Miyata's shirt — which, according to his confession to the investigators, he burned after wrapping the handle of a knife used to fatally stab the victim. The defense team submitted the piece of clothing, along with a forensic analysis stating that the shape of the knife identified as the murder weapon did not match the victim's wound — in seeking the retrial. In 2016, the Kumamoto District Court decided to reopen the trial, judging that given the new evidence, core parts of his confession contradicted the objective facts of the murder.