Mourners left flowers and lit candles near the site of a school shooting in Belgrade on Wednesday.

A 13-year-old opened fire Wednesday at his school in Serbia's capital killing eight fellow students and a school guard before being arrested.

The assailant called the police when the attack was over, though authorities received a call reporting the shooting two minutes earlier.

Police identified the shooter as Kosta Kecmanovic, who attended the Vladislav Ribnikar school, where students would typically range in age from 6 to 15.

Authorities declared three days of nationwide mourning, starting Friday.

Mass shootings are extremely rare in Serbia and in the wider Balkan region; none were reported at schools in recent years. In the last mass shooting, a Balkan war veteran in 2013 killed 13 people in a central Serbian village.