The McWilliams should have been tried for murder, according to the detective who led the John Smith investigation, Operation Oasis.

Detective Inspector Malcolm Bacon, who helped put Brighton child sex fiend Russell Bishop behind bars in 1990, said: "Sussex Police and the Crown Prosecution Service were satisfied from the evidence that John Smith was murdered.

"Whether the McWilliams were responsible should have been put to a jury to decide."

The McWilliams were originally charged with murder but the case failed at the committal stage.

The district judge in Brighton ruled the case should not be sent to crown court because there was no way of proving which of the McWilliams, if either, inflicted the blows that killed John.

Mr Bacon is all too familiar with the impasse.

Last year the detective, MP Des Turner, our crime reporter Phil Mills and concerned mother Sandra Reid met then-Home Secretary Jack Straw to argue for a change in the law.

It followed the acquittal of a Brighton couple accused of murdering two of their babies and a baby nephew, each of them smothered because they cried and "deserved it".

The judge, Mr Justice Moses, ordered the jury to find the couple not guilty because there was insufficient evidence to say which of the defendants had committed the deeds.

He said there was no rational basis on which the jury could decide who was guilty and whether both were at the scene when each baby died.

He concluded: "It is better both be acquitted than one wrongly convicted. You could debate all night the rights and wrongs of it, but that is the law and there are very good reasons for it."

Mr Bacon said: "Assuming all three babies had been murdered, which is the assertion of the police and prosecution, then the law and common sense have parted company."

As in the John Smith case, there were no witnesses but the Crown had proved both accused were in the house at the times the babies died.

Mr Bacon said: "Coincidence, or something more sinister? If three adults went into a room and only two came out alive, leaving one smothered, would the court have made the same ruling?"

The same legal stalemate applied in the case of John and Mr Bacon said the ruling, correct though it was as the law stood, was an insult to common sense.

Former Chief Constable Paul Whitehouse went further after the babies murder case, calling it a loophole that gave callous guardians a licence to kill babies: "It is quite wrong that if two people were present at the scene of a crime both should escape conviction."

He called for an alternative charge to run alongside murder or to stand alone in such cases.

The Argus launched a campaign, backed by Mrs Reid and a 1,000-name petition.

Mr Straw responded by announcing he was considering introducing a new law of killing a child through neglect.

The offence would carry a maximum sentence of 14 years and would apply to cases of joint enterprise where one carried out the deed and the other did not intervene. No proof would be needed to say which one was responsible.

That was last August.

Yesterday, a Home Office spokesman said the proposed new law was still being looked into.

Brighton Kemp Town MP Mr Turner said he was horrified by John Smith's death, the "battery of errors" by social services and the failure of the murder charge.

He said: "I will be contacting the Home Office to renew my call for a change in the law."