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A court decision last week to reopen a 1985 murder trial in Kumamoto Prefecture makes yet another case for requiring prosecutors to disclose all evidence in criminal trials, given the risk that selective use of evidence by investigation authorities can result in wrongful convictions. Koki Miyata, now 83, served 13 years in prison. He is only the latest among people whose guilt for crimes was thrown in doubt by a piece of evidence withheld by the prosecution until after they were convicted and only made open in the process of reopening their cases.

In the absence of material evidence that he killed a man in January 1985, the key to Miyata’s conviction was the confession he made to interrogators. Though he withdrew his confession halfway through the trial and pleaded innocent, the Kumamoto District Court in 1986 gave him 13 years in prison, judging that his confession was voluntary and credible — a decision finalized by the Supreme Court in 1990.

What led the same district court to decide last week to grant Miyata a retrial was new evidence, including an item that contradicted his own statement to the interrogators. Miyata had initially confessed that he tore off a part of his own shirt, wrapped the cloth around a knife that he used to stab the victim so that the weapon would not be blood-stained, and burned the strip of cloth after the crime. Years after he was convicted, however, his lawyers found that the pieces of cloth that made up his whole shirt were intact and in the possession of the prosecutors, who had not submitted them as evidence in his trial.

The strip of cloth that had allegedly been burned was presented to the court upon the demand of Miyata’s lawyers. The court determined that the cloth along with other evidence, such as an expert analysis showing that the shape of the alleged weapon did not match the victim’s wounds — cast doubt over the credibility of his confession. Miyata’s lawyers charged that the prosecutors concealed the existence of the strip of cloth during the trial out of fear that it would expose the contradiction in his confession, and that the 1986 ruling would have been different had that evidence been submitted during the trial.

Whether or not the prosecutors in this case did indeed have the intention alleged by Miyata’s lawyers, evidence that does not support a case established by investigators can be withheld by prosecutors under current rules — including information that may cast doubt on the guilt of the accused.

In a 1967 murder-robbery case in Ibaraki Prefecture, two men who lived near the victim’s house were given life terms — again mostly on the strength of confessions, which they withdrew in court, saying they had been coerced by their interrogators. It was only during proceedings seeking their retrial that prosecutors revealed an account by a witness who said she saw suspicious persons on the evening of the murder near the site who did not look like the accused. The two were cleared of the murder-robbery in a retrial in 2011 — 44 years after their arrest.

In another case, the 2012 release and acquittal of a Nepalese man who had been given a life sentence for the 1997 murder of a Tokyo Electric Power employee was based on a DNA analysis of a piece of evidence — which pointed to the possibility that the crime had been committed by a third party also at the scene — that was disclosed by prosecutors only after his attorneys had sought a retrial.

These are only a few of the examples in which evidence that prosecutors had not originally submitted to the court eventually led to retrials — and acquittals.

Along with mandatory electronic recording of interrogations by investigators, making it mandatory for prosecutors to disclose all evidence at their disposal in criminal trials was one of the key subjects of reform discussions for the criminal justice system since 2011 by the Justice Ministry’s Legislative Council, which were triggered by calls for measures to prevent wrongful charges and convictions. While the legal amendments that came out of the discussions made it mandatory for police and prosecutors to video-record their interrogations in some criminal cases, the decision on whether to require prosecutors to disclose all evidence was eventually shelved — with the prosecutors now obligated only to present to the defense a list of the evidence they have obtained.

Prosecutors remain opposed to disclosing all evidence in their hands — reportedly on the grounds that the accused could use the information to make excuses to their advantage in their trial. But the court decision paving the way for Miyata’s retrial underlines once again why all evidence should be presented to the court — including that which may not support the prosecutors’ case — to ensure a fair trial and eliminate the risk of false convictions. The government needs to reopen the discussions on this issue.