Robert Napper’s guilty plea yesterday to the manslaughter of Rachel Nickell completes a remarkable legal circle. When Colin Stagg was charged with that same brutal killing I was the judge appointed to try a case that excited enormous media coverage. Before the trial in 1994 three things were apparent.

First, the police were faced with overwhelming pressure to identify the killer and establish a compelling case. Second, they were faced with a desperate lack of evidence of any quality against Mr Stagg - their exclusive candidate for the murder – let alone evidence sufficient to establish guilt beyond a reasonable doubt. Finally, it was obvious that the judge would need to be especially wary of the real risk that the jury might be swept along by the tide of widespread hostility to the accused and return a guilty verdict notwithstanding the absence of effective proof.

The second of those features led the police to set up the so-called honey trap, using an undercover policewoman to seduce Mr Stagg into a confession. It proved to be a fruitless initiative. The high-water mark of the material thereby obtained was a single comment by him that might, on one view, have been construed as betraying an awareness of details of the attack that could only have been known to the perpetrator. There was nothing else in the prosecution’s locker. There was no identification, no scientific evidence, no circumstantial evidence and no subsequent incriminating behaviour. Neither was there DNA available either to implicate or to exonerate him. In the event, I ruled that the evidence derived from the entrapment should not go before the jury. It is a graphic measure of the frailty of the prosecution case that, bereft of the foothold offered to them by that rotten plank, they elected to drop their case, and Mr Stagg was acquitted.

Since then a campaign of innuendo has been mounted in sections of the press that has repeatedly invited the public to conclude that Mr Stagg had literally “got away with murder”. The truth, of course, was that he had not got away with anything. He had been singled out because he was a soft target. His appearance, his lifestyle and the libidinous exchanges with the policewoman painted him in singularly unattractive colours.

The police closed their minds to any other possibility than that of his guilt. That cardinal error corrupted the whole of their investigation. They were wrong. I claim no special credit for ruling as I did. I am certain that any other judge in my position would have recognised that proof of guilt was simply not there. To leave the entrapment evidence to the jury would be to open the door to the wholly unacceptable risk that prejudice would replace proof.

There will no doubt be suggestions that there are obvious lessons to be learned from this 14-year saga. I am not so sure. Media hysteria, an embattled police force and the duty of a criminal trial judge to ensure inherent fairness of the process are not novel dimensions in the history

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