A note on what this case is. These killings were a political purge: a leadership group killing its own members over a few weeks, not a series of murders committed by one person against strangers. The case is carried here because it is frequently listed alongside serial murder and readers look for it, and it is marked as outside the definition rather than counted as one.
Hiroko Nagata was born in Tokyo in 1945 and became a central figure in the United Red Army, a small Japanese far-left group formed in 1971 that had retreated to training bases in the mountains of Gunma and Nagano.
Between December 1971 and February 1972 the leadership, principally Nagata and Tsuneo Mori, subjected members to sokatsu, a process of enforced self-criticism. Fourteen members were beaten, bound and left tied outdoors in the mountain winter until they died of the cold and their injuries. The reasons given included wearing make-up, showing insufficient revolutionary spirit, and being pregnant.
It ended when the remaining members fled and five of them took a hostage at a lodge at Asama-Sanso, producing a ten-day siege in February 1972 that was watched live by an enormous Japanese television audience and that destroyed the Japanese radical left as a mass movement.
Nagata was convicted and sentenced to death at the Tokyo District Court on June 18, 1982, upheld in 1993. She was never executed. She developed a brain tumour, and died at the Tokyo Detention House on February 5, 2011, aged sixty-five, after twenty-eight years under sentence.