David Bain verdict: We would do better these days say police

David Bain outside the High Court in Christchurch after jury gave the not guilty verdict. Photo / Simon Baker

Police say that if they were to investigate the Bain murders again they would do things differently.

Southern region commander Malcolm Burgess said police put the best evidence forward - but it was essentially the same as presented in the first trial after the 1994 killings. That investigation was "thorough and impartial".

"As with all investigations, there are things we could do differently and things that we learn," the detective superintendent said.

"However, we need to remember these events happened in 1994. Procedures are different now - there is better forensic testing and improved investigation procedures for dealing with investigations.

"Our role is to put the best evidence available before the court to enable it to reach its decision. We believe we did that."

Mr Burgess said police were disappointed with the outcome but accepted the jury's decision. There was no plan to "re-litigate the evidence in the public arena".

"For police this decision puts an end to the matter."

The moment the Privy Council in London quashed David Bain's murder convictions in May 2007, Detective Inspector Ross Pinkham of Dunedin began delving back 13 years to see what sort of case could be mounted in court against Mr Bain for a second time.

"We were requested by the Solicitor-General to provide him with some advice about where we would go with the investigation and whether the police could provide the Crown with evidence that could be put before the court," Mr Pinkham told the Weekend Herald.

"Really, it was the Solicitor-General's responsibility not to say whether a trial should go ahead, but whether a trial should not go ahead."

Police soon found that despite the passage in time and big advances in technology, they had access to all they needed to go to court again. Mr Pinkham advised Solicitor-General David Collins, QC, who announced on June 21, 2007, that a retrial would take place.

The police's planning for the retrial then became a reality. It meant going back over the evidence that had been put forward when Mr Bain was convicted in 1995 of killing his family.

"I think the biggest task that we had really is to go back to some of the procedures we had in 1994 and realise how much we have come on as far as the quality of our investigations, the quality of the equipment we use for doing some of those investigations," Mr Pinkham said.

"What we really had to do was to bring the 1994 police file into 2007 computerisation."

It took weeks to put "reams and reams" of paperwork, and photographs, on to computer.

Mr Pinkham also put together a new police team to prepare the case for retrial. "We wanted to show independence with our investigation - that we didn't want to be guided just by the staff that had worked on the investigation in 1994 and the trial in 1995."

The exceptions were Detective Senior Sergeant Kallum Croudis, the officer who arrested Mr Bain in 1994, and Detective Sergeant Brett Roberts, who played a minor role in 1994.

Police from around the country travelled to Dunedin to join the investigation, which at its height involved 26 staff.