The internet has quite a few pages available that gives you step by step instructiions. The Anarchist’s Cookbook is also available online as a .pdf file, though the recipies are more likely to kill the would-be bombmaker.
And a search of his computer and ISP should reveal the degree of his interest in bomb making, detonating and timers. I can't imagine him just downloading a recipe and building it without first testing the design somewhere.
The anarchists cookbook is by no means reliable, certainly not for an explosive of the size used in Oslo.