Upon the British surrender of Singapore on 15 February 1942, Shinozaki was "released" by the Twenty-Fifth Army from Changi Prison and went on to become "special adviser" or an interpreter for the Twenty-Fifth Army's Kempeitai in Syonan and supported their actions. After the Pacific War began on 7/8 December 1941, Japanese residents of pre-war Malaya had moved to the Purana Qila internment camp. Among 32 Japanese prisoners of Changi, Shinozaki was the only person familiar with Singapore's political circumstances, so his knowledge was crucial to occupying Japanese forces. He participated in the Sook Ching Massacre as one of the staff who tempted English-speaking Chinese leaders such as Lim Boon Keng, who was captured during the "great inspection", to cooperate with the Japanese Military Administration (JMA). He might have been engaged in the task of checking the list of people who promoted the China Relief Fund and thus who became the target of Kempeitai. According to his autobiography, in his working capacity at the Defence Headquarters, he deliberately stored food supplies at the Thomson Road home of the Little Sisters of the Poor so that the nuns there would have a ready supply of food. In April 1942, he continued to support the Kempeitai by identifying "hostile" residents. Corner wrote that when he was working in Raffles Museum, Shinozaki came to the museum to arrest Corner, because Mrs. Arbenz, a Swiss who was mentally affected by the Japanese occupation, had reported to Shinozaki that Corner was hostile to Japan. As the Special Advisor of Kempeitai, Shinozaki supervised Chinese leaders who were persuaded or forced to interact with JMA by founding The Overseas Chinese Association (OCA), a Japanese-sponsored body started on 2 March 1942 as the main representative of the Chinese community. The OCA was ordered to raise $50 million through compulsory "donations" although Shinozaki denied any involvement in the process in his biography. He mainly managed English-speaking Chinese leaders, though Takase and Wee Twee Kim oppressed Chinese-speaking Chinese leaders during the same period. He also said that he made the list of persons who were not sustainable to the burden of the "donation" before he left the OCA. Until June 1942, during the period when JMA's official staff hadn't arrived from Japan, Shinozaki was relocated to the Syonan municipal office as the Chief Education Officer.