Police were called to a college in Kauhajoki, Western Finland, when a student in his early twenties opened fire with an automatic weapon, killing 10 people.
The gunman, named as Maati Juhani Saari, posted a video of himself last week on YouTube firing a pistol.
Police questioned him about the video the day before the shootings, but decided there was not enough evidence to revoke his firearms licence.
After the shootings, armoured vehicles secured the area around the college.
Police isolated the gunman in one part of the school, where he shot himself in the head, seriously injuring himself, before being arrested.
He was taken to the Tampere University Hospital, where he later died.
The killings prompted the Finnish Prime Minister, Matti Vanhanen, to hold a government press conference over the shootings. He said it was "tragic day" for Finland.