Police in Belgrade, Serbia are reporting that a 7th-grade student who opened fire at his school on Wednesday morning had a list of classmates he intended to kill. The student, identified only as Kosta Kecmanovic, used his father's gun to kill 8 students and a school guard before being arrested. Six other children and a teacher were injured in the attack. The shooting took place at Vladislav Ribnikar primary school in the Vracar neighborhood, on the first day of classes after the May Day holiday. Officials say Kecmanovic had been planning the attack for a month, during which time he drew sketches of the classrooms and composed the list of targets. Serbia has very strict gun laws, but reports indicate there are still tens of thousands of illegal firearms in circulation throughout the country. While mass shootings are rare, experts have long been warning about the potential dangers of having so many weapons in a nation with a history of conflicts and ongoing economic struggles.