A 12-year-old boy was arrested after he opened fire earlier on Tuesday at an elementary school in the city of Vantaa, north of the Finnish capital, Helsinki.
The boy murdered a 6th-grade student and seriously injured two other students.
After the shooting, the boy ran away from school and was later arrested by the police in the suburbs of Vantaa.
The police are investigating the boy's motive, but will not be able to detain him because he is under age 15, the age of criminal liability.
The local police spokesman said that after the child has undergone investigation, he will be transferred to the responsibility of the state welfare services.
Anna-Maja Henriksson, Finland's Minister of Education, called a press conference and burst into tears: "There is a 12-year-old boy who will never come home from school."
Prime Minister Petteri Orpo said that "what is particularly shocking is the age of the victim and the suspect. I assure you that we will carefully investigate the shooting and draw conclusions so that something like this does not happen again."