Like every other citizen of Oslo, I have walked in the streets and buildings that have been blown away. I have even spent time on the island where young political activists were massacred. I share the fear and pain of my country. But the question is always why, and this violence was not blind.

The terror of Norway has not come from Islamic extremists. Nor has it come from the far left, even though both these groups have been accused time after time of being the inner threat to our "way of living". Up to and including the terrifying hours in the afternoon of 22 July, the little terror my country has experienced has come from the far right.

For decades, political violence in this country has been almost the sole preserve of neo-Nazis and other racist groups. During the 1970s they bombed leftwing bookstores and a May Day demonstration. In the 80s two neo-Nazis were executed because they were suspected of betraying the group. In the past two decades, two non-white Norwegian boys have been died as a result of racist attacks. No foreign group has killed or hurt people on Norwegian territory since the second world war, except for the Israeli security force Mossad, which targeted and killed an innocent man by mistake on Lillehammer in 1973.

But even with this history, when this devastating terror hit us, we instantly suspected the Islamic world. It was the jihadis. It had to be.

It was immediately denounced as an attack on Norway, on our way of life. In the streets of Oslo, young women wearing hijabs and Arab-looking men were harassed as soon as the news broke.

Small wonder. For at least 10 years we have been told that terror comes from the east. That an Arab is suspicious, that all Muslims are tainted. We regularly see people of colour being examined in private rooms in airport security; we have endless debates on the limits of "our" tolerance. As the Islamic world has become the Other, we have begun to think of that what differentiates "us" from "them" is the ability to slaughter civilians in cold blood.

There is, of course, another reason why everybody looked for al-Qaida. Norway has been part of the war in Afghanistan for 10 years, we took part in the Iraq war for some time, and we are eager bombers of Tripoli. There is a limit to how long you can partake in war before war reaches you.

But although we all knew it, the war was rarely mentioned when the terrorist hit us. Our first response was rooted in irrationality: it had to be "them". I felt it myself. I feared that the war we took abroad had come to Norway. And what then? What would happen to our society? To tolerance, public debate, and most of all, to our settled immigrants and their Norwegian-born children?

It was not thus. Once again, the heart of darkness lies buried deep within ourselves. The terrorist was a white Nordic male; not a Muslim, but a Muslim hater.

As soon as this was established, the slaughter was discussed as the deed of a mad man; it was no longer seen as primarily an attack on our society. The rhetoric changed, the headlines of the newspapers shifted their focus. Nobody talks about war anymore. When "terrorist" is used, it is most certainly singular, not plural – a particular individual rather than an undefined group which is easily generalised to include sympathisers and anyone else you fancy. The terrible act is now officially a national tragedy. The question is, would it have been thus if the killer was a mad man with an Islamic background?

I also believe that the killer was mad. To hunt down and execute teenagers on an island for an hour, you surely must have taken leave of your senses. But just as 9/11 or the bombing of the subway in London, this is madness with both a clinical and a political cause.

Anyone who has glanced at the web pages of racist groups or followed the online debates of Norwegian newspapers will have seen the rage with which Islamophobia is being spread; the poisonous hatred with which anonymous writers sting anti-racist liberals and the left is only too visible. The 22 July terrorist has participated in many such debates. He has been an active member of one of the biggest Norwegian political parties, the populist right party until 2006. He left them and sought his ideology instead among the community of anti-Islamist groups on the internet.

When the world believed this to be an act of international Islamist terrorism, state leaders, from Obama to Cameron, all stated that they would stand by Norway in our struggle. Which struggle will that be now? All western leaders have the same problem within their own borders. Will they now wage war on homegrown rightwing extremism? On Islamophobia and racism?

Some hours after the bomb blast, the Norwegian prime minister, Jens Stoltenberg, said that our answer to the attack should be more democracy and more openness. Compared to Bush's response to the attacks of 9/11 there is good reason to be proud of this. But in the aftermath of the most dreadful experience in Norway since the second world war I would like to go further. We need to use this incident to strike a blow to the intolerance, racism and hatred that is growing, not just in Norway, nor even only in Scandinavia, but throughout Europe.