During the purge, Nagata, acting as vice-chairman of the URA, directed the killing of twelve members of the group by beatings or by forced exposure to frigid winter air temperatures.

Hiroko Nagata was born in Tokyo and, after graduation from Chofu Gakuen High School, entered Kyoritsu College of Pharmacy (defunct in 2008 and merged into Keio University) to receive training to be a pharmacist.

During her time in college, Nagata became involved full-time in left wing politics, eventually becoming vice-chairman of the United Red Army (URA).

After a series of incidents in which student groups injured or killed law enforcement officials as well as the general public, Japan's National Police Agency cracked down on these organizations, raiding their hideouts and arresting dozens in 1971 and 1972.

Attempting to escape from the police, a core group of radicals from the URA, including Nagata, retreated to a compound in the mountains of Gunma Prefecture during the winter of 1972.

[7] On October 11, 2008, it was revealed that Nagata had fallen into a critical condition due to the tumor, so her family was called for visitation to the Tokyo Detention Center.