Chris Kahui has been found not guilty of murdering his twin babies and the police have announced "no one else" will be charged with the murders. The reason _ sadly _ is simple: to now charge Macsyna King _ or anyone else _ would be to admit they may have got it wrong the first time. This has always been the way the New Zealand police have operated.

Almost 40 years ago, the police were under intense pressure to find the killer of Jeanette and Harvey Crewe. At a time when we had five murders a year and not five a month, the murder of a young couple in their own home was front-page news for weeks.

The initial suspect was Mrs Crewe's father, but police attention then switched to Arthur Thomas, who had once had something of a crush on Mrs Crewe. There was insufficient evidence to charge Thomas, so the police planted some, and two of their number later perjured themselves in court.

Eleven years later, a royal commission of inquiry made the above findings and Thomas was released from prison and paid $1million. The police never re-opened the file and have never admitted to the perjury or the planted evidence.

There are disturbing indications that in a sense, the Kahui trial had similarities with the Thomas one _ although this time there are suggestions that evidence that did not "fit" was ignored, rather than planted, to make it less likely the defence would find it. A complaint is to be filed with the Independent Police Conduct Authority in this regard.

There are two pieces of evidence that are now under scrutiny: cellphone records that show that _ contrary to her alibi _ Macsyna King may have been in Mangere on the night in question, and the way the police dealt with claims by a former boyfriend who claimed King had confessed her guilt to him.

The minuscule time the jurors took to reach their verdict suggests that they not only thought the defence had established reasonable doubt but that a compelling case had been made against Macsyna King.

The Crown case was based on the fact that only Chris Kahui had the opportunity to kill the babies. That theory was based on the police pathologist's conclusions about the time the injuries were inflicted and the supposed fact that King was on the other side of Auckland at the time.

That theory is cast into serious doubt by the evidence of a paediatrician that the injuries could have been inflicted much earlier and the cellphone evidence that shows that King may have been in Mangere the night the killings occurred. The police reaction is that while cellphone records show King was unclear about her whereabouts, it makes no difference because the time she was in Mangere doesn't fit with their pathologist's view of when the injuries occurred.

In cases where a suspect's guilt is unclear, the police are fond of saying that it is not their job to establish guilt, but to put a suspect who they believe to be guilty before the court and let a jury decide. Having done so, they habitually declare their faith in the system, whether the suspect is found guilty or not.

In the Kahui case, the defence produced evidence that suggested Macsyna King may not have been on the far side of Auckland all night and had a medical expert who raised conflicts about the timing of the injuries.

If she faced a trial, Macsyna King might ultimately be found not guilty beyond reasonable doubt. That is not the point; that is our system. On the evidence available, she should at least be put before the court to let another jury decide.

* David Garrett is an Auckland barrister