The curry was served a little before six on the evening of July 25, 1998, at the summer festival of the Sonobe neighborhood in Wakayama, a port city about 280 miles west of Tokyo. Within the hour people were vomiting. Sixty-seven were taken to hospitals with acute arsenic poisoning, and four of them died: Takatoshi Taninaka, sixty-four, and Takaaki Tanaka, fifty-three, the president and vice president of the local residents' council; Miyuki Torii, a sixteen-year-old high school student; and Hirotaka Hayashi, ten, who was no relation to the woman later convicted of killing him. Analysts later calculated that at least 130 grams of arsenic had gone into the communal pot.
The poisoning frightened the whole country. Over the following months Japan saw dozens of copycat cases, and in one of them a man died after drinking canned tea laced with cyanide.
Suspicion in Sonobe settled quickly on a neighbor. Masumi Hayashi, born on July 22, 1961, was thirty-seven, a former insurance saleswoman and the mother of four, and she had helped at the festival. A witness put her beside the pot. Her husband, Kenji, ran a pest extermination business, which meant arsenic in the household. A paper cup pulled from the festival garbage held traces of arsenous acid that investigators said was very similar in makeup to arsenic compounds found among household items at the Hayashi home. And there was a history that investigators began to piece together that summer: the couple had collected on insurance policies after a run of illnesses, and she would eventually be convicted of trying to kill an acquaintance and Kenji himself with arsenic to collect on policies she had taken out on them. Reporters camped outside the house for weeks. A Kyodo photograph from August 1998 shows her in her garden turning a hose on a press crew, and it became the picture of the case.
She was arrested in October 1998 and eventually indicted in nine cases: the curry poisoning, attempted insurance murders, and insurance fraud, some of the fraud counts shared with Kenji. There were also suspicions, never proved, that she had poisoned an employee of hers as far back as 1985. What the prosecution did not have was a confession, a witness who had seen her put anything into the curry, or a clear motive. Prosecutors suggested that she was angry with the other housewives in the neighborhood; the courts never settled the question. The case rested on three things: her opportunity at the pot during a stretch when it was unattended, her record with arsenic, and a trace-element comparison, made with synchrotron radiation, which the prosecution said showed that arsenic found at her home matched the arsenic in the curry. That comparison has been disputed by Japanese scientists ever since.
The Wakayama District Court convicted her and sentenced her to death on December 10, 2002. The Osaka High Court upheld the sentence on June 29, 2005, and on April 21, 2009 the Supreme Court rejected her final appeal; the sentence became final on May 19, making her the eleventh woman sentenced to death in postwar Japan, leaving a death sentence resting, as Kyodo News put it that week, on no direct evidence and no clear motive. She has denied the poisoning from the beginning.
The retrial campaign began almost at once. A first petition, filed in July 2009, was dismissed by the Wakayama District Court in March 2017 and by the Osaka High Court on appeal, and in June 2021 she withdrew her special appeal to the Supreme Court, which ended it. In May 2021 her lawyers filed a second petition with a different theory: that cyanide compounds, not arsenic alone, had killed the four, and that a third party had put them in the pot. The district court rejected it in January 2023. On January 27, 2025 the Osaka High Court, in a decision by Judge Kyoji Ishikawa, rejected her appeal, holding that the cyanide analysis had already been before the trial court and was therefore not new evidence. She took it to the Supreme Court two days later. On November 11, 2025 the Second Petty Bench, presided over by Justice Kazumi Okamura, dismissed that appeal as well.
A third petition, filed with the Wakayama District Court in February 2024 and aimed at the forensic comparison itself, was still pending when that decision came down, and remained pending in August 2026. Among the lawyers now working on her case is Teruo Ikuta, a former judge of the Osaka High Court, a role the Japan Innocence and Death Penalty Information Center described as "very unusual" for a retired judge.
The family has paid its own price. Her son, who speaks publicly under the pseudonym Koji Hayashi, is a truck driver who was a child when she was arrested. He told Agence France-Presse in March 2025 that he was not entirely convinced of her innocence but thought there was "a good chance," and that a retrial was the only way to learn the truth. He said he sometimes imagined the ordinary life he might have had, with marriage, children and a house. On June 9, 2021 her daughter, thirty-seven, jumped from the bridge to Kansai Airport holding her own four-year-old daughter, and both died. Earlier the same day the daughter's eldest child, a girl of sixteen, had been found beaten to death at home. In July 2025 the son and a film director began raising money to build a website about the case.
Her case is now part of a wider argument about retrials in Japan, a system left almost unchanged for a century that critics call the unopenable door. Hopes of reform grew after Iwao Hakamada was acquitted in 2024, forty-two years after he first asked for his case to be reopened, and the government has asked legal experts to review the procedure. In August 2026 she was sixty-five and on death row at the Osaka Detention House, where executions are by hanging and the prisoner learns of it only that morning.