Belgrade: A 13-year-old who shot dead eight fellow students and a security guard at a school in the Serbian capital of Belgrade, made a "kill list" and had planned the attack for weeks, according to police.
The suspect, who is alleged to have used his father's guns -- both of which had legal permits, was arrested shortly after the Wednesday morning attack at the Vladislav Ribnikar primary school in central Belgrade, reports the BBC.
His parents have also been arrested.
In a statement, the police said the boy had planned the attack a month in advance and that he had carried a "priority list" of children to target and which classrooms he would go into first.
Most of the victims were born in 2009 -- meaning they were either 13 or 14 years of age.
The motive for the attack, which also led to the injuries of six students and a teacher, is still being investigated, the police said, adding that the boy was said to have gone to a shooting range more than once with his father before the killings.
In a televised address to the nation on Wednesday night, President Aleksandar Vucic described the attack as "the most difficult day in the modern history of our country".
He said the suspect would be sent to a psychiatric clinic but under current Serbian law, he cannot be held criminally responsible as he is under 14. Vucic has suggested that the age of criminal liability may be lowered to 12 in the wake of the killings.
He has also proposed several other reforms, including an audit on firearms licences and a tightening of the rules around who can access shooting ranges. A national three-day mourning period starting on Friday has been announced.
Mass shootings are comparatively rare in Serbia, which has very strict gun laws, but gun ownership in the country is among the highest in Europe.
The western Balkans are awash with hundreds of thousands of illegal weapons following wars and unrest in the 1990s. In 2019, it was estimated that there are 39.1 firearms per 100 people in Serbia - the third highest in the world, behind the US and Montenegro.
In the deadliest shooting since then, Ljubisa Bogdanovic killed 14 people in the central village of Velika Ivanca in 2013, and Nikola Radosavljevic killed nine and wounded five in the eastern village of Jabukovac in July 2007.