What country did austria Hungary think plotted the attack?

Austria-Hungary believed that Serbia plotted the assassination of Archduke Franz Ferdinand, which occurred on June 28, 1914. The assassination was carried out by Gavrilo Princip, a member of the nationalist group known as the Black Hand, which sought to promote Serbian nationalism. Austria-Hungary viewed Serbia's involvement as a direct threat to its empire, leading to the issuance of an ultimatum and ultimately the outbreak of World War I.