Sweden’s prime minister said the attack at the Risbergska School was the worst mass shooting in country’s history

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."

Sweden is reeling from its worst mass shooting after an armed attacker opened fire at Campus Risbergska, an adult education center in Örebro, on Tuesday, killing at least 11 people, including himself.