On 19 April 1995, Timothy McVeigh parked a van full of fertiliser outside the Alfred P Murrah Federal Building in Oklahoma City, lit a fuse and walked away. The blast killed 168 people, including nineteen children.

McVeigh did it; there’s no doubt about that. Yet an aura of mystery surrounded the case because this 26-year-old decorated veteran didn’t look like the kind of terrorist you see on TV. Some speculated that he took the fall for a wider conspiracy; a few found him rather high-minded. Gore Vidal, who struck up correspondence with McVeigh while he was on death row, regarded him as a misguided defender of the constitution. It helped that he looked good in a jumpsuit.

All this ambiguity about McVeigh, says Jeffrey Toobin, is wrong and dangerous – and the unintended consequence of the federal prosecution strategy. Keen to avoid an O J Simpson-style debacle, federal prosecutors focused on the facts, eschewing the kind of cultural analysis that would have put the murder in context. This went against the instincts of President Bill Clinton, who, coming from Arkansas, was familiar with so-called ‘lone wolves’ like McVeigh and knew that they ran in packs.

The killer hung around gun shows, where he handed out copies of the execrable The Turner Diaries, a racist sci-fi novel that depicts fascists triggering a race war by setting off a bomb packed with fertiliser. His stated casus belli were the bloody federal raids on the Weaver family in