The dead were four members of the community: Takatoshi Taninaka, sixty-four, and Takaaki Tanaka, fifty-three, who served as council president and vice president of their local association; Hirotaka Hayashi, ten years old; and Miyuki Torii, sixteen. The poisoning struck at the heart of what a matsuri is supposed to represent -- communal trust, shared food, neighbors gathering in good faith. The scale of the crime was staggering. Sixty-three survivors suffered from acute arsenic poisoning, a condition that begins with severe gastrointestinal distress and can cause lasting organ damage. That the poison was arsenic, an old and unmistakable toxin, pointed investigators toward someone with ready access to the substance.

Suspicion fell quickly on Masumi Hayashi, a thirty-seven-year-old former insurance saleswoman who lived in the neighborhood. A witness had seen her near the curry pots during the window between preparation and serving. Her husband worked as an insect exterminator, giving the household easy access to arsenic. After her arrest three months later, the case expanded in disturbing directions. Hayashi and her husband were indicted on multiple insurance fraud charges. Investigators linked her to three other attempted poisonings over the previous decade, each tied to life-insurance payoffs. She was believed to have tried to poison her own husband at least once. A blue paper cup recovered from the festival garbage contained traces of arsenous acid whose chemical composition closely matched arsenic samples found in the Hayashi home. Her alleged motive for poisoning the curry: anger at neighbors who had been shunning her family.

Hayashi pleaded innocent. Her defense lawyers, including the prominent attorney Yoshihiro Yasuda, argued that the prosecution's case rested entirely on circumstantial evidence -- no one saw her put arsenic in the curry, and the chemical analysis showed the substances were "very similar" rather than identical. Wakayama District Court was unconvinced and sentenced her to death in 2002. Osaka High Court upheld the sentence on June 29, 2005. On April 21, 2009, the Supreme Court of Japan rejected her final appeal. The case became a touchstone in Japan's ongoing debate about capital punishment and the standard of proof required to impose it, particularly in a legal system where confessions carry enormous weight and Hayashi never confessed.

Hayashi continued to maintain her innocence from death row. She formally petitioned for a retrial in July 2009. Wakayama District Court rejected that petition in March 2017. She appealed to Osaka High Court in April 2017 and was again rejected. A third petition for retrial was filed in June 2021. The case has cast a long shadow over the Sonobe community and beyond. The Wakayama curry poisoning remains one of the most discussed criminal cases in modern Japan, a reminder that the most ordinary rituals of community life -- cooking together, eating together, gathering under paper lanterns on a summer evening -- depend on a fragile trust that, once broken, is extraordinarily difficult to restore.