The Shizuoka District Court ruled on Thursday that investigators had fabricated evidence against Iwao Hakamata, who was convicted of killing a miso company executive, his wife and their two children in Shizuoka Prefecture.
Presiding Judge Koshi Kunii said, "He cannot be identified as the culprit," citing the principle of giving the defendant the benefit of the doubt in criminal trials.
The court found that key evidence, including clothing allegedly worn by Hakamata during the crime, had been planted by investigators. It also determined that Hakamata's confession was coerced through "inhumane" interrogation methods.
Hakamata, who was released from prison in 2014 after new evidence emerged, was recognized that year as the world's longest-serving death row inmate by Guinness World Records.