Newly discovered official documents show the wartime Japanese military forcibly recruited females abroad into sexual servitude as "comfort women," a Japanese professor who discovered the materials said Thursday, questioning why the evidence wasn't revealed at the time of Tokyo's 1993 apology.

Hirofumi Hayashi, a professor of modern Japanese history at Kanto Gakuin University, found trial documents at the National Archives of Japan relating to six cases heard before tribunals set up for Class-B and Class-C war criminals after the end of World War II by China's Nationalist Party and the Netherlands, then the colonial ruler of the Dutch East Indies (present-day Indonesia).

The materials had been kept by the Justice Ministry, but were transferred to the archives in 1999 or later.