The 13-year-old ‘star pupil’ who confessed to shooting dead eight of his classmates at a school in Serbia was allegedly bullied and made a gun pose with his fingers in his last Instagram post before carrying out the massacre.

Kosta Kecmanovic, 13, allegedly opened fire on his screaming classmates inside their classroom in the Vladislav Ribnikar Elementary School, killing seven girls and a boy – all below the age of 14.

A security guard, identified as Dragon Vlahovic, in his early 50s, was also killed in the mass shooting, while a further six pupils and a history teacher were critically wounded in the attack on Wednesday morning.

The baby-faced teenager, who may not be legally responsible for his actions due to being under the age of 14, was arrested by Serbian police in the school’s playground and led away with his face covered after he called police confessing to the murders.

Hours before carrying out the attack, Kecmanovic posted a sinister photograph of himself smiling and making a gun pose with his fingers on Instagram.

Kecmanovic, described as a ‘star pupil’ who won prizes in maths, was armed with two guns and two petrol bombs had drawn up plans for the massacre a month beforehand. The plan included a list of children he wanted to kill and their classes and a map of the school layout, police said. 

‘The sketch looks like something from a video game or a horror movie, which indicates that he planned in detail, by classes, who to liquidate,’ Belgrade’s police chief, Veselin Milic, said.

‘After the crime, he called the police. He worked out a plan for entering the school and leaving the school. He determined the priority targets,’ he added.

Serbia’s President Aleksandar Vučić said on Wednesday night that both the boy’s parents – both doctors – have been arrested, and that he is to be taken to a psychiatric institution. 

Terrified students hid under their desks amid ‘non-stop shooting’ at around 8.40am on Wednesday morning.

At least eight children and a security guard were killed in the gun rampage and there are fears that the death toll could rise even further, with some sustaining life-threatening injuries.

The shooter first killed a guard at the school in central Belgrade and then three students in a hallway, police said. 

He then entered a classroom – reportedly choosing it simply because it was close to the entrance – and opened fire again.

Kecmanovic then called police himself and as officers put handcuffs on him, he reportedly told local media he had shot his classmates ‘because I am a psychopath’.

Anxious parents rushed to the school after being told of the shooting, waiting for news of their children.

As mothers and fathers were told their children were among those killed, they staggered backwards in utter disbelief that their child who had left their home that morning was not coming back.

Their screams and wails tore through the silence, as many collapsed in grief at hearing the horrific fate of their children.

Two of the six children who were wounded in the attack are now fighting to stay alive after being shot in the neck and head. The injured teacher, Tatjana Stevanović, in her early 50s, was also ‘in danger’ after being shot in the stomach and hands.

Kecmanovic stole his father’s two guns and assembled two petrol bombs in preparation of the attack. His father, a famous radiologist at a Belgrade private school, was arrested on suspicion of aggravated endangering of the public safety.

Police have not stated a motivation for the attack, but parents of children at the school have said he was bullied while Kecmanovic’s father, who has not been named, said the boy often told him he did not fit into society.

According to Serbian legal provisions, the 13-year-old boy ‘is deemed criminally irresponsible, because he has not reached the age of 14’, local media has reported. 

Gun ownership is widespread in Serbia, which has witnessed several mass shootings over the past decade, and President Aleksandar Vucic said checks would be stepped up.

As Serbia prepares for three days of national mourning, Vucic announced a moratorium on new gun licenses other than for hunting, revision of existing permits and surveillance of shooting ranges and how civilians store their weapons. School shootings are rare.

The shooter, who gave himself up to police and at 13 is below Serbia’s age of criminal responsibility, will be placed in a psychiatric institution, Vucic told reporters, adding that both his father and mother had been arrested.

‘He was waiting for this day. He was at the shooting range with his father three times,’ Vucic said. The boy had asked for a transfer to another class where he had three friends, he said.

A drawing by the alleged shooter, which was shown to reporters, looked like ‘something from a video game or a horror movie,’ Milic said, ‘which indicates that he planned in detail, by classes, whom to liquidate.’

Most students were able to flee through a back door, according to a local official. 

Milan Milosevic, a father of one of the pupils, said his daughter was in the history class where the shooter opened fire ‘randomly’ at other children as they cowered under their desks.

‘She managed to escape,’ the father told Serbian TV station N1.

‘He [the shooter] fired first at the teacher and then the children who ducked under the desks,’ Milosevic quoted his daughter as saying. 

‘They say he [the shooter] was quiet and a good pupil. He recently joined their class.’ 

Mr Milosevic said that he rushed out to the school when he heard what had happened.

‘I asked where is my child but no one could tell me anything at first,’ he said. ‘Then she called and we found out she was out.’

‘I saw the security guard lying under the table. I saw two girls with blood on their shirts,’ Mr Milosevic added.

Evgenija, 14, said she knew the suspected gunman and described him as ‘somehow silent… [he] appeared nice and had good grades’. 

‘[I] did not know much about him, he was not that open to everyone. I would never expect that this could happen,’ she told reporters.

‘I heard noises and I thought some boys, some kids were throwing firecrackers… But then I saw the security guard falling to the ground,’ she said, adding that she then ran away.

Serbia’s Interior Ministry said in an updated statement that eight children and a security guard were killed in the shooting, while six children and one school teacher were wounded. 

‘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.’ 

A student who was in a sports class downstairs when the gunfire erupted said: ‘I was able to hear the shooting. It was non-stop.’

‘I didn’t know what was happening. We were receiving some messages on the phone.’ 

The student, who heard the violence unfold, identified only by her initials, E.M. because of her age, described the suspect as a ‘quiet guy’ who ‘looked nice.’

‘He was having good grades, but we didn’t know much about him,’ the student added. ‘He was not so open with everybody. Surely I wasn’t expecting this to happen. ‘

Milan Nedeljkovic, mayor of the central Vracar district where the school is located, said doctors were fighting to save a teacher’s life.

Mr Nedeljkovic said the school’s security guard likely prevented more deaths by putting himself in front of the shooter.

The guard ‘wanted to prevent the tragedy and he was the first victim,’ Nedeljkovic told reporters told journalists live on television outside the school.

‘I saw kids running out from the school, screaming. Parents came, they were in panic. Later I heard three shots,’ a girl who attends a high school adjacent to Vladislav Ribnikar told state TV RTS. 

Police sealed off the blocks around the school, in the center of Belgrade.

Officers in helmets and bulletproof vests cordoned off the area around the school, which is in the Vračar neighbourhood in central Belgrade.

Local media footage from the scene showed commotion outside the school as police removed the suspect, whose head was covered as officers led him to a car parked in the street.

An investigation into the motives behind the shooting is under way. 

Serbia’s Interior Ministry said in a statement: ‘The police sent all available patrols immediately to the spot and arrested a suspected minor – a seventh grade student who is suspected of firing several shots from his father’s gun in the direction of students and school security.’

Vračar is a wealthy area of the city and a number of embassies are based there. 

A row of ambulances were pictured parked on Kralja Milutin Street outside.

Police sealed off the blocks surrounding the school. Primary schools in Serbia have eight grades. 

Mass shootings in the country are extremely rare. In the last mass shooting, a Balkan war veteran in 2013 killed 13 people in a central Serbian village.

Experts, however, have repeatedly warned of the number of weapons left over in the country after the wars of the 1990s.

The western Balkans are awash with hundreds of thousands of illegal weapons following the unrest there.

Serbian authorities have offered several amnesties for owners to hand in or register illegal guns.