It was about 12:30 p.m. on a gray Tuesday in Orebro, Sweden, when gunfire erupted at an adult education center, with students and teachers in class. Minutes later, as an alarm wailed, the police charged into the center, Campus Risbergska, where they encountered a chaotic, smoke-filled scene. It would be hours before they gave an all-clear.

“An inferno. Dead people. Injured people. Screams and smoke,” Lars Wiren, Orebro’s police chief, said Thursday at a news conference as he described the scene.

The shooting in Orebro, a quiet university town in central Sweden that has become a haven for migrant communities, has left the country reeling. The national government has described the attack as the worst mass shooting in Sweden’s history, and flags around the country are flying at half-staff. In the days after the attack, the authorities are still seeking to understand why a man entered the campus and opened fire. At least 11 people were found dead, the police said, and the suspect was believed to be among them.

The police have not publicly identified the gunman or shared any details about a possible motive. Swedish news outlets have identified him as Rickard Andersson, a 35-year-old who lived alone in an apartment near the school.

The police have not confirmed the reports, and The New York Times has yet to independently confirm the gunman’s identity. Officials have begun to share how the attack unfolded, describing a heavily armed assailant who worked alone.