Yet again we have acquittals of people falsely charged and convicted based on wrongful confessions coerced by investigators. In this case, a 52-year-old Osaka woman and her former partner spent 20 years behind bars for arson and the murder of her 11-year-old daughter in 1995, until their retrial plea filed in 2009 was eventually endorsed last year and led to their release. The decision Wednesday by the Osaka District Court finding Keiko Aoki and Tatsuhiro Boku innocent must be followed up by a thorough examination by both the investigation authorities and the judiciary to find out why the prosecution's case against the pair — based almost entirely on confessions made during interrogation that were retracted in court — went unchallenged.

The prosecution's case held that Aoki and Boku, arrested shortly after the July 1995 death of the girl in a fire at their home in Osaka, had conspired to kill her for the benefits from a life insurance scheme taken out on the victim — that Aoki made her daughter take a bath, and then Boku sprayed gasoline in the garage next to the bathroom and set it on fire with a lighter. In the absence of material evidence, the key to the case was a confession that Boku allegedly made to interrogators detailing how he set the garage on fire, along with a statement by Aoki acknowledging her own complicity. Even though they pleaded innocent throughout their trials, the Osaka District Court in 1999 handed down a life term for both — a decision endorsed by the Osaka High Court in 2004 and finalized by the Supreme Court in 2006.

Their 2009 retrial plea was approved by the Osaka District Court in 2012, a decision challenged by prosecutors but endorsed in October 2015 by the Osaka High Court, which ordered that their prison terms be suspended and they be freed. What proved key to reopening the case was a test performed by their lawyers — and later by the prosecution themselves — to re-enact the scene of the alleged arson based on the account that Boku gave to investigators. The result — in both the defense and prosecution tests — clearly contradicted what he said during interrogation, thus putting the credibility of his confession in doubt. The defense test instead pointed to the possibility — also endorsed in the district court decision this week — that the fire was caused accidentally by gasoline leaking from the tank of a vehicle in the garage that was set alight by the pilot light of the bathtub water heater.