In the winter of 1971 and 1972, at training bases in the mountains of Gunma Prefecture, the leaders of Japan's United Red Army turned on their own members. They called it sokatsu, a process of enforced self-criticism meant to produce true revolutionaries. In practice it meant beatings, and members tied to posts outside in the mountain cold until they died of exposure and their injuries; others were beaten to death or killed with knives. Twelve members died between late December and February 12, 1972. The two people who ran it were the group's chairman, Tsuneo Mori, and its vice-chair, Hiroko Nagata.
Nagata was born in Tokyo on February 8, 1945, and became a leader of one of the militant factions that merged in 1971 to form the United Red Army. According to the court's findings, she had already conspired that August in the killing of two members who tried to leave the group. The purge began that December. One of the first to die was Mitsuo Ozaki, who died two days after his self-criticism began on December 28; another, Kato, was beaten, tied to a post outside for more beatings until Nagata and Mori judged his self-criticism complete, and died of his injuries on January 4. Accounts of the purge record reasons as slight as a woman wearing make-up. A woman who was pregnant was among the dead. Some accounts also count a non-member who was present and killed.
Nagata was arrested on February 16, 1972. Days later five of the remaining members fled to the Asama-Sanso lodge at Karuizawa in Nagano and took the wife of the lodge manager hostage. The ten-day siege and the gun battles with police were broadcast live to an enormous audience, and three people, two police officers and a civilian, were killed before the police stormed the lodge. The hostage survived. Only afterward did the full story of the killings in the mountains come out, and with it the Japanese far left lost what public support it still had. Mori hanged himself in the Tokyo Detention House in 1973, at the age of twenty-eight.
At first Nagata denied the charges, but she gradually admitted her part and wept in court, saying, "Even I had human emotions," the Mainichi reported. The Tokyo District Court sentenced her to death on June 18, 1982. The Tokyo High Court upheld the sentence, and on February 19, 1993, so did the Supreme Court. A request for a retrial was rejected on November 28, 2006. In prison she wrote several books and drew a support group.
She had surgery for a brain tumor in 1984. In 2006 she collapsed at the detention house with brain atrophy and impaired consciousness and was moved to a medical prison in Hachioji; she returned the following year and was bedridden from then on. In October 2008 her family was called to her bedside. She died of brain cancer at the Tokyo Detention House on the evening of February 5, 2011, aged sixty-five, twenty-nine years after she was sentenced. The sentence was never carried out.