"A song which played in the suspect's car is known as a marching anthem for Serbian nationalist paramilitary units known as Chetniks during the 1992-95 Bosnian war. It praises Bosnian Serb leader Radovan Karadzic, who was convicted of genocide and war crimes."
(Clashes between Bosnian Muslims, Serbs and Croats started in late February 1992)
https://www.bbc.com/news/world-asia-47579243
After the Allied victory in World War II, Yugoslavia was set up as a federation of six republics, with borders drawn along ethnic and historical lines: Bosnia and Herzegovina, Croatia, Macedonia, Montenegro, Serbia, and Slovenia.
The Bosnian War was part of the breakup of Yugoslavia. It involved muslim control and fighting but was not majorly a separation into white and muslim states or muslim control: rather it was a breakup of the "federation" during political upheavals with muslims as a factor of many factors.
https://en.wikipedia.org/wiki/Socialist_Federal_Republic_of_Yugoslavia
(note to millenials - this could be playin in sympathy OR in motivation for attack - be careful drawing conclusions. also note the source, bbc, is guilty of some fake news and audio can EASILY be dubbed over. the authenticity of it all is exactly not verified. perhaps the video is, whether edited, we don't know)