Despite the coroner pointing the finger of blame at Chris Kahui, it is unlikely he could ever be tried again for the murder of his twin sons.

Auckland University law professor Warren Brookbanks said the only way Mr Kahui could be charged with the murders again would be if “dramatic” new evidence against him emerged.

In a case such as the deaths of 3-month-old twins Chris and Cru, in which there was no "smoking gun" evidence that could prove who killed them, it would take a confession to reopen the case, he said.

This is because of New Zealand's "double jeopardy" laws, enshrined in the Bill of Rights Act, which protect people against the “patent injustice” of being punished twice for the same offence.

However, in 2008 Parliament agreed there were exceptional circumstances in which a second trial could be appropriate. Those circumstances include a "tainted acquittal" due to perjury, bribery or fabricated evidence.

Someone could also be tried a second time if new and compelling evidence came to light.

But that was a high threshold to meet, Mr Brookbanks said.

“It would have to be something in the nature of a confession or some very powerful evidence that points towards the guilt of the person that's been acquitted.

"It's likely to be fairly rarely the case that such evidence would come forward, certainly after a major trial where the police have put a lot of resources into getting a conviction in the first place.

"It would have to be something out of left field that was completely unanticipated or unknown at the time of the original prosecution.”

There have been no cases yet in New Zealand of a second trial for murder after an acquittal because of fresh evidence.

In the wake of coroner Garry Evans' findings, there is the possibility that perjury charges could be laid against Mr Kahui. The maximum penalty for committing perjury is seven years' imprisonment. Police did not respond to questions about whether they would consider laying any new charges.

It is also highly unlikely that a civil action could be brought against Mr Kahui.

Auckland University law professor Bill Hodge said ACC legislation basically ruled out the possibility of suing where death or personal injury has taken place.

“We're not in OJ Simpson-type territory. Remember OJ Simpson was acquitted of two murders and then in the American system a civil case could be brought.

"In New Zealand, because of ACC and also because of the Law Reform Act, you can't sue for personal injury or death or punitives for someone who's dead. So I would say the civil side is absolutely a dead duck.”

LANDMARK DECISION RAISES SOME QUESTIONS

The landmark ruling implicating Chris Kahui in the deaths of his twin babies raises questions about what his acquittal means, the country's chief coroner says.

"Implicit in this is a very serious allegation - ‘he did it'," Judge Neil MacLean said.

"That in turn raises an interesting debate about what does a not guilty verdict mean. Essentially it often doesn't mean ‘innocent'. It means ‘not proven'."

The coronial findings are in clear contrast to the outcome of the 2008 High Court trial that acquitted Mr Kahui of the boys' murders.

"This is a very stark example of how two different judicial processes following different paths can arrive at what are apparently two different conclusions," Judge MacLean said.

"The coronial process is about what is the truth. It's driven by the coroner . . . saying, ‘I'm investigating this on behalf of the dead babies, on behalf of the public, to find out what really happened here'."

The criminal process, by contrast, was about, "has the Crown proven beyond reasonable doubt the commission of a particular crime - in this case murder".

He labelled Mr Evans' report a landmark child abuse decision that would be of immense interest to coroners around the Commonwealth.

"It says, ‘I am aware there's been a criminal process. I'm aware there's been an acquittal'. He's had an advantage the court didn't have - that Chris Kahui actually gave evidence."

- © Fairfax NZ News