Sweden’s worst mass shooting has left at least 11 people dead, including the gunman, at an adult education center as officials warned that the death toll could rise.

The suspect, named in reports as 35-year-old local man Rickard Andersson, was reported to be a former student of the school in Orebo, a city 157 km (98 miles) west of Stockholm, where the attack took place on Tuesday. Eleven people died in the shooting, including the attacker, with at least six others injured.

Officials in Sweden have vowed to determine why a man killed 10 people, and apparently himself, in an unprecedented attack that's shaken their "society to its core."