In a meticulously planned attack, a 13-year-old boy who opened fire at his school in the Serbian capital on Wednesday made sketches of the classrooms and a list of the kids he intended to target, according to police. Before calling the police and being taken into custody, he killed eight other students and a guard.

Mass shootings are extremely uncommon in the Balkan region, despite the fact that Serbia is awash in weapons from the 1990s wars. There haven’t been any reported mass shootings at Serbian schools recently.

According to senior police official Veselin Milic, the shooter killed a security guard at the Vladislav Ribnikar school in central Belgrade before killing three students in a hallway. He then went into a history class near the school’s entrance and started shooting.

Ljiljana Radicevic told The Associated Press that her granddaughter was also killed in the shooting. Ana was near the school entrance when the assailant shot the school guard, “and then he shot at my Ana,” Radicevic said. “As soon as she did not answer, I knew it was over.” Radicevic did not provide Ana’s full name or age.

Six children and a teacher were also hospitalized. Two children remained in serious condition after hourslong surgeries, doctors said later Wednesday.

The assailant called police himself after the shooting was over. Authorities also received a call reporting the shooting two minutes earlier.