Death-row inmate Hiroko Nagata, who participated in the early 1970s mass murder of her comrades in the now-defunct United Red Army, died at the Tokyo Detention House at the age of 65 Saturday evening after a long battle with brain cancer, sources said Sunday.

Nagata underwent surgery for a brain tumor in 1984. In 2006, she collapsed at the detention facility after suffering from brain atrophy and impaired consciousness, and was transferred to a medical prison in the city of Hachioji in western Tokyo.

She was returned to the detention house in 2007 and had been bedridden in recent years.

Nagata was a conspirator in the August 1971 murders of two members who tried to leave the radical group. She was also involved in the mass killing of 12 more members in a mountainous area of Gunma Prefecture between December 1971 and February 1972 over ideological differences.

Nagata was arrested in February 1972, and was sentenced to death by the Tokyo District and High courts. The lower court sentences were upheld by the Supreme Court in 1993.

After her arrest, five members of the group, including Hiroshi Sakaguchi, 64, barricaded themselves at the Asama Lodge in Karuizawa, Nagano Prefecture, taking the wife of the lodge manager hostage. The ensuing gunbattles with police, in which three officers were killed, were played out in front of television cameras over the following 10 days.