A recent district court decision to exonerate a former assistant nurse who was wrongly convicted of murder and spent 12 years in prison is a scathing indictment of the nation’s criminal justice system.

In a March 31 ruling, the Otsu District Court acquitted Mika Nishiyama, 40, who served her full sentence after being falsely accused of murdering a 72-year-old patient in 2003. The court said her confession was unreliable since it had been extracted through an illegal investigation.

The court also pointed out that the male patient at Koto Memorial Hospital in Higashi-Omi, Shiga Prefecture, could have died from disease and his death had not even been verified as a homicide.

Nishiyama was sentenced to 12 years in prison for killing the patient by weaning him from ventilator support at the hospital. On her second request, the Osaka High Court in December 2017 granted her a retrial and sent the case back to the district court.

The latest court decision has confirmed that the case against the defendant was a house built on sand.

All people involved in criminal justice in Japan need to learn lessons from this miscarriage of justice and take steps to avoid making the same mistake.

The new trial focused on the cause of death. The ruling questioned the credibility of the expert opinion about the cause of death that was used as key evidence against the defendant.

The court said the view that the patient died of oxygen deficit caused by being taken off the ventilator tube was not quite consistent with the autopsy report, the process of the medical treatment for the patient or testimonies of other nurses.

Nishiyama confessed that she took the patient off the ventilator tube. But she repeatedly and significantly changed her remarks, which the ruling said was because of leading questions by police interrogators.

According to the ruling, Nishiyama has mild developmental disorders, which make her feel compelled to satisfy the needs of others. Police took advantage of her feelings of affection toward an investigator who spoke kindly to her and helped elicit many confession statements in line with the police narrative.

The years between her arrest in 2004 and her exoneration underscore afresh the danger of criminal investigations heavily dependent on the defendant’s confessions.

But police and prosecutors have yet to apologize to Nishiyama nor sought her acquittal during the retrial.

Now that a court ruling has officially called the investigation into the case seriously flawed, law enforcement authorities should make every effort to clarify why the probe was so unfair and faulty as to force Nishiyama to suffer injustice for so long and publish the findings of their inquiry.

Some problems common to past cases of wrongful convictions have come to light.

One is investigators’ attempt to cover up inconvenient evidence. Before arresting Nishiyama, police compiled an investigation report on an expert medical witness testimony that the patient might have died of natural causes, including choking on phlegm.

But this report was sent to prosecutors only last summer after the court granted a retrial. This caused prosecutors to drop their plan to seek to prove her guilt again during the retrial and decided not to present a new case against her.

If the report had been disclosed earlier--before her indictment, during the original trial or after her first request for a retrial, for instance--things could have turned out differently.

The exoneration has also highlighted afresh serious shortcomings of the procedures for a retrial, especially a lack of clear rules concerning the ways evidence should be treated or the hearings should be held.

After declaring Nishiyama innocent, Presiding Judge Naoki Onishi said many serious questions had been raised about the ways criminal investigations are conducted and trials are held as well as the nation’s criminal justice system itself.

“All people involved should take these issues as their own and make efforts for improvement,” he said.

These remarks should lead to actions that really make a difference.

--The Asahi Shimbun, April 4