Witnesses described chaos and panic as Auvinen shot dead his headmistress, five boys, two girls, and wounded a dozen others as they tried to flee the carnage.
Internet warning
Miro Lukinmaa, a student, told the Iltalehti newspaper: "Suddenly people began running and shots were heard and began raining down.
Auvinen had signalled his intentions in
a video posted on the internet [AFP]
"I saw injured people lying in the corridor. We started to run and followed [the crowd] in panic. Everyone was trying to squeeze through a narrow door."
The shooting came after a video entitled "Jokela High School Massacre - 11/7/2007" was posted on the video-sharing website YouTube.
The video shows a still photo of a low building that appears to be the Jokela High School.
The photo then breaks apart to reveal a red-tinted picture of a man pointing a handgun at the camera.
"He [Auvinen] was moving systematically through the school hallways, knocking on the doors and shooting through the doors," said Kim Kiuru, who was teaching a grade 8 class when the shooting began.
"It felt unreal, a pupil I have taught myself was running towards me, screaming, a pistol in his hand."
Hannu Joensivusaid, the mayor of Tuusula, said: "This is a peaceful place, nothing like this has happened and nothing like this is to be expected either."
Despite having the world's third-largest per capita handgun ownership, violent incidents are rare at Finnish schools.
Tuusula is a town of 35,000, around 60km from the capital, Helsinki.