Alexander I Obrenovich and his wife Draga Mashin were assassinated in the Royal Palace 
in Belgrade by dissident Serbian Army officers.

ON the night of April 10th, 1903 King Alexander and Quenn Draga of Serbia were killed in their palace Their naked bodies were thrown out palace window. They were not the only people killed that night; also killed were Serbian Prime Minister, the Minister of War, two of the queens brothers and 12 members of the palace guard. It was the most brutal assignations to take place in Europe in recent history and much of Europe was appalled

In the immediate aftermath of the assassination the people of Belgrade celebrated. Alexander who had started his reign as a reformer had turned into a tyrant. One of the triggers of the assassination was the decision of Alexander a week before his assassination to suspend the liberal constitution which he had originally been one of the strongest supporters of. The constitution provided for secret ballots as well as freedom the Press.

The asgsisintion was masterminded by Colonel Mashin who was the brother of the the queens first husband and Colonel Dragutin Dimitryevich. Mashin blamed the Queen for his brothers death. But the personal issues went back a generation to a feed between the Obrenovich and Karageorgevich dynasties both families were instrumental in founding Serbia, and they alternated ruling Serbia.

On the death of the Alexander Peter Karageorgevic became the new King. What his involvement in the assassination was never determined. Afterward in an interview with to the press from his home in exile in Geneva he said:
I formally disapprove of violent measures. I especially deplore the fact that the army had to recourse to such measures- an army which has nobler tasks to accomplish than assassinations. It would have sufficed to force Alexander to sign an abdication. He could have been bound, as has been done in other circumstances. It was a horrible thing to shed his blood.
You ask me what my additive will be when I an in the possession of the Crown? Well do you offer me the Crown? Take it for granted that if I am called to the thrown, I shall not fail to take inspiration from the admirable institutions in Switzerland which I have learned to appreciate highly.
I am in favor of absolute liberty of the press, and I hope to Serbia prosper under the regime of the Constitution of 1889, which is very liberal..

Alexander went on to pardon everyone involved on political violence during the period before he began his reign. Dimitryevich went on the found Black Hand, and extremely nationalistic Serbian organization that was responsible in 1914 of the assassination of Archduke Franz Ferdinand in Sarajevo in 1914