A teenager who killed eight fellow students and a security guard in a Serbian school planned the attack for weeks and had a "kill list", according to police.
The 13-year-old was arrested following Wednesday morning's attack at a primary school in central Belgrade.
Another six pupils and a teacher were also injured in the shooting.
Police say the motive for the attack is still being investigated.
The suspect, named by police as Kosta Kecmanovic, is alleged to have used his father's guns, both of which had legal permits.
He is also said to have gone to a shooting range more than once with his father before the killings.
The boy's mother and father have since been arrested.
Most of the victims are 13 and 14 years old.
A national three-day mourning period starting on Friday has been announced.
Source: BBC News
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