@cnn: Protesters in Serbia were holding a moment of silence for 15 people killed in a train station collapse when suddenly, the crowd went into a panic. Rights groups and opposition officials allege that security forces deployed a sonic weapon - illegal in the country. The government denies the allegations. CNN spoke to multiple audio forensics experts as more than half a million petitioners call on the Serbian government to investigate if illegal sonic weapons were used. #cnn #news #serbia #sonic