A total of 80 postmortem exams have been conducted over the past decade on prison inmates who died of unknown causes, Justice Minister Mayumi Moriyama said Friday.

According to death records kept at each prison, as required under the Prison Law, 260 inmates died between 1993 and 2002 at Fuchu Prison, in western Tokyo; Yokosuka Prison, in Kanagawa Prefecture; and the Nagoya and Osaka prisons.

Autopsies were conducted in eight of the cases, including two inmates at Nagoya Prison who were later found to have been killed by guards.