Conversation so far:
Are there any other interesting aspects about the Franz Joseph I of Autria article?
the assassination of Franz Joseph's  nephew and heir-presumptive, Archduke Franz Ferdinand, in Sarajevo resulted in Austria-Hungary's declaration of war against the Kingdom of Serbia
When did  occur the assassination of his nephew and heir-presumptive, Archduke Franz Ferdinand, in Sarajevo that  resulted in Austria-Hungary's declaration of war against the Kingdom of Serbia?
On June 28, 1914
How did the assassination of his nephew and heir-presumptive, Archduke Franz Ferdinand, in Sarajevo that resulted in Austria-Hungary's declaration of war against the Kingdom of Serbia that contributed to the out break of the war On June 28, 1914?
it activated a system of alliances which resulted in World War I.

Question: Who assassinated him?
Self-contained rewrite: Who assassinated Franz Joseph I of Autria's nephew Archduke Franz Ferdinand?