At least eight pupils and a security guard were killed at a school in Belgrade when a seventh-grade student opened fire on them in the morning on May 3, Serbian police have confirmed.

A 13-year-old student at Vladislav Ribnikar elementary school in the Vracar neighborhood in downtown Belgrade, with the initials K. K., who is suspected of having committed this crime was arrested in the school yard.

Six children and a teacher were seriously injured and are currently receiving treatment at the Emergency Center and in Tirsova clinic in Belgrade, the police said.

According to reports, K. K. had been planning the attack for a long time. Serbian public broadcaster RTS reported that the shooter brought a gun and a small-caliber pistol to the school, which he had taken from his father’s home, as well as four Molotov cocktails.

The motive for the attack is still unknown, and the police are investigating the shooting. 

"All police forces are still on the ground and are intensively working to shed light on all the facts and circumstances that led to this tragedy," the police said.

The father of the boy who committed the crime has been arrested, as confirmed by Minister of Interior Bratilav Gašić. The minister stated that the father claimed to have kept the weapon securely locked and had obtained the necessary legal permits for it. However, both pistols, for which licenses were issued in 2016 and 2017, were found and it appears that the child had access to the safe code.

Additionally, according to unofficial information, the child had previously gone to a shooting range with his father. The minister announced that legal measures will be taken against the father.

According to RTS reports, four patients, three students and a teacher, were admitted to the Emergency Center, all with gunshot wounds. The students are around 13 years old, while the teacher was born in 1970.

One student is in critical condition, with serious gunshot wounds to the chest and neck. Another student has a gunshot wound in the left lower leg, while the other has wounds in the stomach and both hands.

The teacher was wounded in the stomach and both hands. A team of neurosurgeons from the Emergency Center performed surgery on a child who had a severe gunshot wound to the head.

The government has decided that May 5, 6 and 7 will be days of mourning in Serbia.

Updated to add information on the arrest of the suspect's father.