The head of Interpol has defended Finnish police over accusations that they blundered in allowing a disaffected trainee chef to keep his handgun permit despite posting violent videos on YouTube.

It was a fateful decision. Yesterday morning, less than 24 hours after he was interrogated and let free, 22-year-old Matti Saari went on a rampage through a hospitality college in the town of Kauhajoki, killing ten people before turning his gun on himself.

The massacre came just ten months after Pekka-Eric Auvinen, 18, went on a shooting spree at Jokela High School near Helsinki, killing eight people including his headmistress.

In retrospect at least, all the signs were there for a copycat killing. Both Auvinen and Saari posted violent videos on YouTube, both identified themselves by the name of their favourite group and year of birth; both had a morbid fascination with the Columbine school massacre of 1999.

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After a second gun massacre in a Finnish classroom this proud Nordic country must ask itself searching questions

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But for Ronald Noble, secretary-general of Interpol, hindsight is too easy - and foresight is still impossible.

“It’s unfair to expect police to be able to be clairvoyant like the movie Minority Report and know whether or not someone making a video intends to commit harm consistent with that video,” Mr Noble said today, referring to the 2002 Steven Spielberg film in which an elite law enforcement squad is able to predict crimes before they happen.

“People will be second-guessing,” he added. “Knowing now that he killed these people, you look at the video - it looks even more frightening. So now you say, ’How is it that they let him go? How is it that they didn’t arrest him? How is it that they didn’t put him in observation in a psychiatric ward for three days?”’

Finland has one of the world's highest rates of gun ownership and some of Europe's most relaxed gun laws - even 15-year-olds can obtain guns for target shooting or hunting - although the country's President and Prime Minister have said that they will need to be made stricter after the two school massacres.

Mr Noble suggested that part of the the answer might be a regulatory code allowing police to revoke the firearm licence of anyone who showed signs that they might pose a threat - as happened with Saari, the Kauhajoki killer. “Then police can say, ’OK, we don’t have enough to arrest you but we are certainly going to take your firearms away,”’ he said.

With a full inquiry into their decisions hanging over them, police officers were working today to identify the charred victims of yesterday's massacre. Apart from the Walther P22 he showed off on YouTube, Saari was also armed with petrol bombs that he used to burn the bodies of his victims.

Elsewhere in Finland there was a sense of shock, reflected on newspaper front pages. The main national daily, Helsingin Sanomat, replaced its usual front-page advertisement with a large picture of a woman adding a candle to a memorial in front of the school. The text above a picture of Saari read “Why?”

“The web cannot be held responsible for this, but you can certainly ask how much the web feeds the dark side of human nature,” the paper said in an editorial.

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