Japanese occupation forces in the area had begun to disarm and disband the Japanese-trained, Pembela Tanah Air (PETA) Indonesian units as soon as 18 August. The discharged officers and personnel were then recruited into the Badan Keamanan Rakyat (People's Security Agency, BKR), the new armed forces of the nationalist government. Around late August and early September, some of the nationalist youths (pemuda) began to seize arms from Japanese forces – in some cases involving murders, but largely through simple disarmament and in some cases voluntarily. Looting against Chinese and Eurasians of the city also began to occur.
