A 22-year-old woman was killed and five people were injured in a shooting at a rave in the northern Swiss town of Aarau, local police said. The attack occurred in the early hours of Sunday at a techno party at a covered horse-racing track. The woman, an Italian citizen, died at the scene, while all those injured were Swiss residents in their 20s.

Police appealed for witnesses to provide any images of the incident and cordoned off large parts of the town as they searched for the attackers. “We have no definite information about who is behind the attack,” police spokesperson Bernhard Graser told Reuters. “We don’t know if it’s one, if it’s several people, if they are on the run by vehicle or on foot.”

The shooting occurred at around 2:30 a.m. after the music stopped. A 34-year-old witness, who asked to remain anonymous, said he initially mistook the sounds for fireworks. Some people took cover behind a DJ booth, and one woman hid behind a refrigerator but was hit in the back by a bullet and bled to death despite efforts to revive her. “It’s just incredibly tragic. She was young,” he said. “That something like this could happen in Aarau, at a local event, is simply unimaginable. I still can’t really process it.”

As a precaution, police increased their presence beyond the town, which is about 50 km west of Zurich and 30 km south of the German border. Graser said there were indications the shooter or shooters were no longer in the immediate area, but police continued their search across the town and the canton. Reuters footage showed armed officers patrolling, police convoys moving through the streets, and armoured vehicles parked near the crime scene.

Organisers of the annual rave expressed shock and heartbreak over the incident. “A rave should always be a place of joy and love, never a place where people are killed, injured, or left in fear,” they said. Switzerland has one of the highest rates of gun ownership in Europe, although violent shootings are rare. The country approved tighter gun control rules in 2019.