Voja Tankosic, a major in the Serbian Army, was one of the founders of the Black Hand group. Tankosic worked closely with Dragutin Dimitrijevic, in the 1903 military coup that brought King Peter to power. During the Balkan Wars(1912-13) Tankosic developed a reputation as an outstanding partisan fighter. He was rewarded by becoming the commanding officer of Serbia's guerrilla academy at Nis.
Tankosic and Dragutin Dimitrijevic were involved in the plot in 1911 to assassinate Emperor Franz Josef. When this failed, they turned their attention to the the heir to the throne, Archduke Franz Ferdinand. The men were concerned about Ferdinand's plans to grant concessions to the South Slavs. The leaders of the Black Hand feared that if this happened, an independent Serbian state would be more difficult to achieve.
When Dimitrijevic heard that Archduke Franz Ferdinand was planning to visit Sarajevo in June 1914, he sent three members of the Black Hand group, Gavrilo Princip, Nedjelko Cabrinovic and Trifko Grabez from Serbia to assassinate him. Nikola Pasic, the prime minister of Serbia, Pasic heard about the plot and gave instructions for the three men to be arrested. However, his orders were not implemented and Archduke Franz Ferdinand was assassinated.
Several members of the Black Hand group interrogated by the Austrian authorities claimed that three men from Serbia, Tankosic, Dragutin Dimitrijevic and Milan Ciganovic had organised the plot. On 25th July, 1914, the Austro-Hungarian government demanded that the Serbian government arrest the men and send them to face trial in Vienna.
On 25th July, 1914, Nikola Pasic, the prime minister of Serbia, told the Austro-Hungarian government that he was unable to hand over these three men as it "would be a violation of Serbia's Constitution and criminal in law". Three days later Austro-Hungarian declared war on Serbia.
I, in joining the organisation "Union or Death", swear by the Sun that warms me, by the Earth that nourishes me, before God, by the blood of the ancestors, on my honour and on my life, that I will from this moment until my death be faithful to the laws of this organisation; and that I will always be ready to make any sacrifice for it.
I swear before God, on my honour and on my life, that I will take all the secrets of this organisation into my grave with me.
Tankosic was a secondary figure. The chief culprit, if one wants to use the word culprit, was Ciganovic.
There is nothing to show the complicity of the Serbian government in the direction of the assassination or its preparations or in supplying of weapons. On the contrary, there is evidence that would appear to show complicity is out of the question.
If the intentions (war with Serbia) prevailing at my departure still exist, demands might be extended for: (1) Suppression of complicity of Serbian government government officials in smuggling persons and material across the frontier. (2) Dismissal of Serbian frontier officers at Sabac and Loznica for smuggling.