ORIGINAL: Curtis Lemay
You keep claim ONE civilian was the Serb Government.
There were multiple assassination attempts that very day. So, at a minimum, it was more than one person. And we don't know if the Serb Government was involved, but the assassins were pursuing Serb national interests - so, they were at least a proxy.
Regardless, Serbs took the first belligerent act.
It can be argued that Austria-Hungary's annexation of Bosnia in 1908 was the 'first belligerent act'.
The annexation was a violation of the 1878 Treaty of Berlin and provoked a general European crisis, including mobilization, that only ended in April 1909, when Serbia and Russia backed down.
The Bosnian Crisis of 1908–09, also known as the Annexation crisis (German: Bosnische Annexionskrise, Bosnian: Aneksiona kriza) or the First Balkan Crisis, erupted in early October 1908 when Austria-Hungary announced the annexation of Bosnia and Herzegovina, territories formerly within the sovereignty of the Ottoman Empire.[a] This unilateral action—timed to coincide with Bulgaria's declaration of independence (5 October) from the Ottoman Empire—sparked protestations from all the Great Powers and Austria-Hungary's Balkan neighbours, Serbia and Montenegro. In April 1909 the Treaty of Berlin was amended to reflect the fait accompli and bring the crisis to an end. The crisis permanently damaged relations between Austria-Hungary on one hand, and Italy, Serbia, and the Russian Empire on the other. It helped lay the grounds for World War I. Although the crisis ended with what appeared to be a total Austro-Hungarian diplomatic victory, Russia became determined not to back down again and hastened its military build-up. Austrian–Serbian relations became permanently stressed. https://en.wikipedia.org/wiki/Bosnian_Crisis
Ironically, Franz Ferdinand might not have been in Sarajevo if not for the annexation.