All day Saturday, hundreds of thousands of citizens marched through downtown Belgrade in the largest student rally Serbia has seen since the start of protests last November.
The largely peaceful gathering had just entered its seventh hour when students called on the crowd to observe a 15-minute silence to honour the 15 people who were killed when the canopy over the entrance to Novi Sad railway station collapsed on November 1.
People lit up the darkness with their phones, and everyone fell silent.
Then, at precisely 7:11 p.m., panic ensued as a loud noise suddenly came out of nowhere, and people began to flee.
Some videos shared on social media show groups of people suddenly splitting in two or people fleeing in panic, as though they were being chased.
Intense panic and disorientation
“It sounded like a crazy rumbling, like a jet flying overhead,” Miroslav Lukic told DW. “But it wasn’t deafeningly loud—more like a distant, threatening noise.”
“It sounded like an aeroplane was landing, coming from the direction of the Presidential Palace,” said Dusan Simin.
“I had the impression that huge armoured vehicles were approaching,” Bojana Milanovic told DW.
“It felt like some invisible wave that split us to the left and right,” recalled Jelena Ristanovic. “The eye couldn’t see anything, but the body felt intense panic and disorientation.”
A loud, strange noise and vibrations
DW spoke with about a dozen people who were on the streets in downtown Belgrade on Saturday evening. Every one of them described hearing a brief, loud, strange noise and vibrations that made them feel as though danger was approaching.
“We couldn’t escape it; we didn’t know what to do,” said Dusan Simin. “You didn’t know if something would fall on your head or if you’d be hit from the side. We fell over one another. My wife hit her head on a pole. I was watching her but couldn’t help. We still feel uneasy.”
Jelena Ristanovic was also disorientated: “When it happened, I instinctively pulled the hood of my jacket over my head,” she said. “My legs gave way for a while.”
“I was really scared, and I ran about 20–30 meters,” said Miroslav Lukic. “When a man next to me started yelling ‘They can’t kill us all,’ I came to my senses and began to look around to see what was happening.”
Bojana Milanovic reported feeling confused and panicked: “I didn’t know where to hide, and I felt like someone was chasing us,” she said. “When we stopped and saw nothing was wrong, we looked at each other and asked what had happened.”
Was a sound cannon deployed?
Milanovic is not alone in this: Everyone in Serbia wants to know what it was that interrupted the 15-minute silence in Belgrade on Saturday.
Military expert Aleksandar Radic was one of the first to suggest that a so-called “sound cannon” had been used against the protesters.
“The reactions of the people show that they were affected by infrasound,” he told DW. “Some people have symptoms typical of such a situation. One piece of indirect proof is the fact that pro-government supporters gathered in Pionirski Park were each given an umbrella to protect against low-frequency sounds.”
This theory is supported by Professor Zoran Maksimovic of the Faculty of Dramatic Arts at the University of Arts in Belgrade, who teaches courses related to sound.
“It’s basically just a regular speaker, but specially designed to be directed and extremely loud. It has a very long range—up to several kilometres,” he explained to DW.
Maksimovic says that music, speech, a sound effect like a flying jet or a specifically generated frequency signal can be played using this speaker.
Or was it a vortex cannon?
However, experts from the international organization Earshot argue that based on their analysis of videos provided by the Center for Research, Transparency and Accountability (CRTA), the sound is “consistent with the noise produced by a Vortex Ring Gun or Vortex Cannon.”
This weapon, they say, expels gas from a cylinder at high speed, producing a noise similar to that of a jet engine.
Maksimovic, however, casts doubt on this theory because, he says, such devices are large and unwieldy, whereas the “sound cannon” comes in various models and can be operated by a single person.
Would the use of such a device be legal?
Radic backs up his theory with claims that Serbia purchased a sound cannon from the American company Genesis in 2022.
“It was sold by a company from the US to an Israeli firm, which then sold it to a private company in Serbia, which then sold it to a state-owned enterprise responsible for procuring strategic resources, Jugoimport,” Radic asserted in an interview with DW, adding that there is written documentation, but that it is confidential.
But did the authorities have the right to use such a device against protesters? Radic argues that they did not, as it is not on the list of equipment designated for crowd control in Serbia’s Law on Internal Affairs.
The government attempted to amend this law in 2022, but the changes were not adopted.
“But the real problem with legality is that no prior warning was given and no reason for the application of such a device,” said Radic. “You must give a warning before applying any police powers. The other issue is that this device was used when people were at rest.”
Vucic dismisses claims as lies
So far, all Serbian authorities have denied that any acoustic weaponry was used on Saturday.
Serbian President Aleksandar Vucic has said that neither the Serbian Army nor the Military Police Special Unit “Cobras” possess a sound cannon.
He has pledged to investigate those he claims are spreading lies about the use of such a weapon and accuses organizations such as CRTA and Earshot of lying.
“CRTA is a non-governmental organization largely funded by British, American, Swiss, Swedish, and other sources,” Vucic posted on Instagram. “You won’t defeat Serbia with lies. We won’t let you escape with your lies about the acoustic cannon.”
Former Prime Minister Milos Vucevic, who resigned at the end of January, has said that the government is ready to officially invite the US Federal Bureau of Investigation and Russia’s Federal Security Service, FSB, to Serbia to investigate the claims.
Meanwhile, pro-government media are reporting security service claims that the panic was caused by student marshals. Students have denied such theories.
People seek medical assistance
In the days after the rally, many sought medical assistance for ongoing symptoms.
“I went to the doctor on Sunday because I felt weak and uneasy,” Bojana Milanovic told DW. “Other people in the waiting room were saying they felt dizzy, had difficulty breathing and their pulses were racing. Many said they had a ringing in their ears and hearing problems” she said.
Media reports indicate that police officers have visited health centres and doctors’ surgeries in response to citizens’ complaints, collecting statements and photographing documentation.
Two doctors confirmed to DW that the police had come, but said that they had been too busy with patients to know exactly what the officers were doing.
Dusan Simin’s wife, who hit her head on a pole during the chaos, received medication and was referred to a psychiatrist.
Simin himself plans to take legal action. “We will seek justice,” he said, “because whatever happened, it really was not normal.”