How many acoustic weapons does the Serbian government have and did it use them on protesters?

Anti-corruption protestors in the Serbian capital were quietly standing still, observing 15 minutes of silence on 15 March.

They were paying tribute to 16 people killed in November when a concrete canopy collapsed at a railway station in Novi Sad, northern Serbia. But suddenly, they scattered, screaming.

Watching videos taken at the scene, it is not clear what causes the protesters to flee. Sara Babic was at the vigil when she heard something she finds hard to describe.

"We have never experienced something like that," she told Sky News. "It was like some vehicle, like an aeroplane, the kind that's massive, and you don't have a chance to survive it.

It was like an army that is coming so fast and there are a million of them. "It started like a human stampede, people were running… and then people started falling and screaming and panicking.

And the next thing someone is saying, calm down, and we look behind us, and we cannot see anything." Protesters and human rights groups in Serbia say the cause was a powerful acoustic sound device used illegally. Immediately after the incident, interior minister Ivica Dacic denied Serbia had any long-range acoustic devices (LRADs).

These can be used as powerful speakers to communicate with large crowds. But they can also be used to direct painful levels of sound at people in their range.

In a parliamentary session on 18 March, Mr Dacic admitted the government did have a device, an LRAD 100X, but insisted it had not been used. And just a day later, at a press conference in Brussels, Serbian President Aleksandar Vucic said if it was proved that a sonic weapon was used at the rally, he would resign.

However, also on 19 March, a picture posted by a prominent opposition politician Marinika Tepic appeared to show Serbian police with a more powerful acoustic device - a LRAD 450XL - outside the Serbian National Assembly on the day of the protest, less than 600 metres from where crowds had gathered. Her post matched a picture taken by a local media outlet.

Mr Dacic followed with a new statement confirming the vehicle by the National Assembly had been equipped with an LRAD device, but he said it had not been moved, and the device had not been used. On the same day, the Serbian interior ministry published photos showing a vehicle mounted with an LRAD 450XL.

Tepic's opposition Party of Freedom and Justice held a press conference later that day, where she revealed documents appearing to show the interior ministry, under former minister Aleksandar Vulin, requested to buy 16 LRAD devices. The documents show the ministry paid 2,464,469 Serbian dinar (around £24,464 at current exchange rates) each for the LRAD 100X devices before VAT, and 6,201,300 Serbian dinar (around £61,558 today) each for the LRAD 450XL.

This amounted to a total cost of more than £600,000 at current exchange rates. The Party of Freedom and Justice say they are unable to disclose the source of the documents for security reasons.

When asked, Genasys, a US company that manufactures the LRAD 100X and LRAD 450XL models, did not disclose if it had sold LRAD devices to Romax Trade, a trading company registered in Novi Sad, but told Sky News: "The video and audio evidence we have seen and heard does not support the use of an LRAD during the March 15th incident in Belgrade, Serbia." The Serbian government did not respond to Sky News' request for comment on the use or purchase of acoustic devices. Mr Vucic on 16 April stated in a public address that the Russian security service, the FSB, who were invited to investigate the incident, had concluded that acoustic devices of the LRAD types possessed by Serbian police were not used.

The Romax Trade website shows the Serbian Ministry of the Interior (MUP) as a "significant partner". Romax have a licence from the Serbian ministry of trade, tourism, and telecommunications to import and export arms and military equipment.

The tax ID number and the company number on the licence match those on the documents published by Tepic. Romax Trade also has certifications for their access to confidential information from the Serbian government office of national security.

Romax Trade did not respond to Sky News' request for comment. Controlling protesters The Serbian Law on Interior does not permit the use of acoustic weapons against citizens.

In 2022, the Ministry of the Interior prepared a draft law which would have added "a device for the emission of sound waves" as an explicitly endorsed measure. The law was not adopted.

LRADs are not categorized as a weapon in the US and so do not require a US export licence. According to the Genasys website, their LRAD systems are used in more than 100 countries around the world.

Speaking on Sky News, Serbian ambassador to the UK Goran Aleksic said independent experts were invited to Serbia to investigate reports that the Serbian government used an acoustic weapon against a peaceful crowd. "According to the statements of our government officials, the President, the minister of the interior, nothing was used at that day," Aleksic told Sky's Yalda Hakim.

Following the incident on 15 March, Serbian rights groups collated more than 3,000 statements from people who said they experienced the incident and presented them to the European Court of Human Rights. The devices have a microphone for speech, inputs for playback of recordings, and deterrent tones based on frequencies most painful to the human ear.

Users can direct this in a beam of sound to target and disperse crowds. Police sound weapons scholar Daphne Carr explains the presence of an LRAD at a protest can be threatening for protestors, who do not know if the device will be used to issue instructions or to use the painful deterrent tone.

"This object is a dual use technology and the use of it as a communications function and as a weapon is a convenient way in which the makers and users of the device can deflect any negative attention," Carr said. In 2023, the UN Special Rapporteur on torture added acoustic devices to the list of goods recommended to be regulated at national and international levels.

Laura Kauer, an editor of Lethal in Disguise, a report on how crowd control devices impact health and human rights, is concerned about the secrecy surrounding LRADs. "There is very little information on how [LRADs] are tested and developed, they tend to be developed in a military setting and we're not sure when we're going to see it on the streets until an incident happens," Kauer told Sky News.

That was the case for Sara Babic, who attended the protest in Belgrade. She said: "I was shocked because I didn't know that something like that exists.

I never heard of it. I didn't know that our government has it." Because LRADs are sold by private companies, and trade in them does not require export licenses, in many cases protestors have no idea if their government or local police force owns an LRAD until one is used against them.

"There's no transparency, there's no mechanism at the international level that lets you know who is producing what and what's being sold where," Kauer said. Sonic Injuries The Genasys LRAD 450XL manual states it "is capable of producing sound pressure levels that have the potential to cause temporary or permanent hearing damage if not used properly".

120 decibels are considered the average human pain threshold, and the maximum sound of an LRAD 100X is 140 decibels, while the LRAD 450XL reaches 145 decibels. Prolonged exposure to loud noise can cause permanent hearing loss.

Dr Rohini Haar, a medical advisor for Physicians for Human Rights, told Sky News: "The chilling effect on the right to free speech or to protest is that people get afraid that they're going to be in pain, or these weapons are going to be used against them. They have this sense of fear, then they may not even actually go to a protest." The Data and Forensics team is a multi-skilled unit dedicated to providing transparent journalism from Sky News.

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