Subsequently he visited tribal communities around Taiwan and interviewed surviving members of the Volunteers, resulting in the publication of Testimonies, as well as a volume of photography entitled A History of the Rule of the Colony of Taiwan.
之後又到台灣各部落遍訪尚活在人世的義勇隊員，集結成《證言》及《台灣植民地統治史》照片集一冊，是已發表有關高砂義勇隊最完整的三本史料。