Jemima Lewis: We need the law to save us from ourselves

When Tony Blair says the law is not serving up the justice that people want, he assumes this is a bad thing

Stagg - as if you could have forgotten - is the man once suspected of murdering Rachel Nickell on Wimbledon Common 14 years ago. The case against him was thrown out of court, the judge pronouncing himself aghast at the flimsiness of the prosecution's case. But in the court of the public imagination, as presided over by the press, Stagg was guilty as charged.

So stubborn was the stain on his reputation that, in 2003, the acquitted man begged the police to take a DNA sample from him, so that it could be compared with a trace found on Nickell's clothing. Sure enough, after a breakthrough in DNA testing, the police have identified a new prime suspect: they are questioning a 40-year-old Broadmoor inmate, serving time for another murder.

Yet Stagg's mood could hardly be described as triumphant. "I've always been associated with the Rachel Nickell case and I'll never shake that off, really," he gloomily predicted this week. "You will always have people who believe I had something to do with it. They'll just think there's no smoke without fire."

This is probably true, even though a cursory review of the evidence suggests there should never have been any smoke in the first place. The whole case was a will-o'-the-wisp, conjured from the fevered imaginations of the police. There was no forensic evidence linking Stagg to the murder. He was merely someone who happened to live nearby, and who had been spotted - along with countless other men - walking his dog on the Common half an hour before Nickell's murder.

He was, however, guilty of one thing: being a bit weird. He hadn't had much luck with girls, despite lifting weights. He was a follower of the pagan cult Wicca. His flat was painted black, and he owned a leather-studded belt and a collection of nudie pictures.

Bad interior decor and romantic inadequacy are not - yet - crimes. But it was Stagg's misfortune to be going through his gothic period at a time when Cracker was on the telly and "psychological profiling" was all the rage. The police hired a man described as the "real-life Cracker", forensic psychologist Paul Britton, to help to solve the Nickell murder. His profile of the killer - disorganised, unpopular, none too bright - convinced them that they'd found their man.

The trouble with an idée fixe is precisely that - it can't be budged. The lack of evidence against Stagg only strengthened the determination of the police to get him. A female PC was deployed to become his "pen pal", wooing him with sexual promises in exchange for his confidences. She pretended to be turned on by murder, and he - smitten by this miraculous beauty who had somehow dropped into his lap - obliged by making up bloodthirsty fantasies for her. Finally, she announced she was ready to sleep with him - but only if he was the Wimbledon Common Murderer. "I'm sorry," he said, "but I'm not."

Ah, but we all knew better. Not just the pig-headed police, or the unscrupulous red-tops, or the ignorant masses: there was hardly a soul in Britain who didn't think Stagg was a bit iffy. When he was acquitted, there were terrible lamentations - not because an innocent man had been vilified, but because police bungling had left him free to kill again.

Shortly after his acquittal, Stagg took to walking his dog in Richmond Park, where my father takes his daily constitutional. Whenever their paths crossed, Stagg would make a cap-doffing gesture at my father and say: "Morning, Squire."

The first time this happened it caused a sensation in our family. My father was chiefly excited that anyone, suspected sex murderer or no, should have called him Squire. But for my sister and me, it was the vicarious brush with evil that caused our eyes to pop: the very notion of our bookish, corduroy-clad father making contact with such a mythical ogre, and living to tell the tale. "Did you see Colin Stagg today?" we would clamour, wide-eyed and vibrating with fear, like Brownies trading ghost stories around the camp fire. "What did he look like? Was he sinister?"

It shames me now to think how eagerly I assumed - almost willed - him to be guilty. But this is what we humans do: make psychological profiles based on instinct and prejudice. We rush to judgement, revel in it, refuse to relinquish it, even when the hard facts point elsewhere.

When Tony Blair says the law is not serving up the kind of justice that people want, he assumes this is a bad thing. But the people's justice is hasty, mean-spirited and based on vague feelings in the bones. We need the cold hand of the law to save us from ourselves. The statue of Justice outside the Old Bailey is blindfolded for a reason: because true justice is not swayed by appearances, let alone the colour of a man's walls.

jemima.lewis@virgin.net