Chetnik units engaged in mass murders and war crimes. In 1991, the Croatian town of Erdut was forcefully taken over by the SDG and JNA and annexed to the puppet state of Republic of Serbian Krajina. Croats and other non-Serbs were either expelled or killed with Serbs repopulating empty villages in the area. On 1 April 1992, the SDG attacked Bijeljina and carried out a massacre of Muslim civilians. On 4 April, Chetnik irregulars helped the JNA in shelling Sarajevo. On 6 April, Chetniks and the JNA attacked Bijeljina, Foča, Bratunac, and Višegrad. On 9 April, the SDG and Šešelj's Chetniks aided the JNA and special units of the Serbian security force in overtaking Zvornik and ridding it of its local Muslim population.