The suspect put videos of himself on YouTube
Matti Juhani Saari was known to Finnish police before he decided to turn his guns on his fellow students, killing ten people, then himself.
The 22-year-old culinary arts student was interviewed just one day before the killings, after he posted four clips on video-sharing website YouTube.
The 20-30 seconds long video clips show a man dressed in black or dark colours, firing a handgun in rapid succession at an apparent shooting range.
"You will die next," he calls as he fires the first few shots, looking assured and pleased with himself.
The videos were posted on Friday, five days before the shooting at the Kauhajoki vocational school.
A message posted alongside said: "Whole life is war and whole life is pain. And you will fight alone in your personal war."
Among his interests, the Kauhajoki resident had listed computers, guns, sex and beer. Horror movies were among his favourites.
The YouTube user's profile, which has now been taken down, included the words: "And suddenly there was war and the mothers they screamed. For revenge and reprisals for another war."
The lyrics apparently come from the song War by German Goth band Wumpscut - which Mr Saari had adapted to use on his YouTube profile.
He signed himself on YouTube as "Wumpscut86", the number possibly referring to his date of birth.
Among his favourite videos were clips from the 1999 Columbine school shootings in Colorado, US, that left 13 people dead.
Police began investigations soon after the posting.
They managed to reach Mr Saari on Monday, and he was invited to come in for an interview regarding the video.
He held a temporary firearms certificate issued in August, but police did not have "enough evidence to revoke the suspect's gun licence", Interior Minister Anne Holmlund told a news conference.
"Naturally, we will now investigate the police operation to see if mistakes were made," the minister said.
Many Finns will be shocked at the apparent similarity with Pekka-Eric Auvinen, the 18-year-old student who opened fire at his high school in southern Finland last November, killing eight people.
Auvinen had left a suicide note for his family and warned of his attack in video messages posted on YouTube.