Watch video posted by the YouTube killer

The teenager who killed eight people in a high school shooting in southern Finland was a social outcast who was bullied at school, a senior police official said today.

Tero Haapala, a detective investigating the massacre at Jokela high school in Tuusula, said that Pekka-Eric Auvinen, 18, appeared to have chosen his victims at random rather than selecting people against whom he had a grievance. "You can say that the motive is still open," Detective Superintendent Haapala said. "But the explanation can be found mainly in his web writings and his social behaviour."

He added that Auvinen had been determined to kill as many people as possible in an attempt to create a spectacle before he turned the gun on himself. The killer died in hospital from a head wound hours after the attack.

Investigators believe that the killer revealed plans for the massacre in postings on YouTube and on his own website. He appears in a video grinning at the camera after shooting at apples, apparently as target practice. Documents signed by Auvinen urge revolution and the extinction of humanity.

Another document, entitled "Attack information" and posted at 11.45pm the night before the attacks, describes in detail how and when the "mass murder" will take place, including the .22 calibre weapon that the killer would use.

Auvinen's name was appended to a "manifesto" posted on the internet that claims that "humanity is overrated" and that "it's time to put natural selection and survival of the fittest back on tracks". Auvinen's profile on YouTube, written under the pseudonym Sturmgeist89, concludes: "I am the law, judge and executioner. There is no higher authority than me."

Local reports said that the victims were five boys, two girls and a woman. It is unclear whether the woman is the school's headmistress, or, as Mr Haapala said this morning, the school nurse. About a dozen other people were injured as they attempted to escape the mayhem.

Police have sealed off the school for the rest of the week, with conscripts from Helsinki's Santahamina garrison standing guard.

Grieving students placed candles outside the school, which was being examined by forensic officers attempting to reconstruct the shooting spree that sent panicked students and teachers fleeing for their lives.

Police lines have been drawn at a distance of about 100m from the school complex. Two Pasi armoured personnel carriers were spotted at a nearby fire station in Tuusula, which is 30 miles north of Helsinki. The school's flag, like those at public buildings throughout the country, flew at half-mast.

Witnesses described a scene of mayhem in the leafy lakeside community, in which the assailant scoured the school for victims while shouting “revolution”.

A day of mourning was declared in Finland, which is unaccustomed to deadly shootings despite a high rate of gun ownership. A study by the International Action Network on Small Arms in 2005 put the number of legally owned guns at 1.6 million, the equivalent of one gun for every three people.

Memorial services were planned across Finland including in Tuusula, where a church was turned into a crisis center with experts on hand to comfort grieving residents.

Police chief Matti Tohkanen said that Auvinen had belonged to a gun club and obtained a licence for the pistol on October 19. He had no previous criminal record and was from an "ordinary family”.

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