A great deal has been written about Columbine, but never before has there been a book in which the whole case – the shooting, the events leading up to it and its aftermath – is reconstructed and analysed in such detail as in Tim Krabbé’s We Are But We Aren’t Psycho. Having meticulously researched the abundant original material (including tens of thousands of pages of witness statements, and the school essays and journals of the perpetrators), he is able to refute myths, discover flaws in the police report and contradict much of what we thought we knew about Columbine.

Many different groups have used Columbine as propaganda: the anti-gun lobby, religious fanatics, anti-bullying crusaders, critics of violent media. Harris and Klebold ranted about anger and revenge, the non-existence of good and evil, the wish to be united with a girl in death, the brainless robots and zombies of our society who do not deserve to live – but not even they seemed to know exactly why they were doing it.

The reality is that no simple cause can be singled out. How did two intelligent boys from loving, intact, upper middle class families manage to convince themselves they needed to become mass murderers? Columbine is often regarded as an unsolvable riddle. More often still it is seen as an open-and-shut case: two bullied outcasts took revenge; an evil psychopathic mastermind duped a depressed follower into committing an atrocity.

Krabbé shows convincingly that the truth was stranger and more sinister: two friends lured each other onto a deadly path and found themselves compelled to follow it to the end. Columbine was caused by the chance meeting of two shockingly normal but very different boys: one who bragged about mass murder and saw his own death as part of the bargain; one who longed for an afterlife with a girl and saw mass murder as a way to die.

We Are But We Aren’t Psycho rightfully claims to be the definitive book on Columbine. It is an important historical document, a literary masterpiece and a gripping story in one. It is also a showcase of clues on how to prevent new Columbines.

• Consistently reserving judgement and separating myth from reality, Krabbé shows how the two teenagers were powerless to stop their fantasies turning into action.
• Tim Krabbé: ‘I quickly realized that the subject was too interesting for anovel.’