A former police officer's mistake that helped convince the Privy Council to order a retrial of David Bain has come under scrutiny in the High Court at Christchurch.
David Bain, 37, is accused of shooting his father Robin, mother Margaret, brother Stephen and sisters Arawa and Laniet in their Dunedin home on 20 June 1994.
The defence says Robin Bain killed the family members present in the house before using the accused's rifle to shoot himself.
The Crown's case continued on Monday as the trial entered its fourth week.
Milton Weir, a detective sergeant in 1994, was in charge of part of the investigation that led to David Bain's arrest and subsequent conviction for the murders.
Mr Weir told the court on Monday he was "absolutely shocked" to discover that he had misled the jury in David Bain's first trial in 1995.
Mr Bain was convicted of murdering his family, but the Privy Council later said Mr Weir's incorrect evidence was one of nine points that may have contributed to that conviction.
Mr Weir told the jury that a lens from a pair of eye glasses was found in a different part of Stephen Bain's bedroom to where it actually was.
The lens is a crucial piece of evidence for the Crown, which says David Bain left it in Stephen Bain's bedroom as the pair fought, before Stephen was shot dead.
On Monday, Mr Weir admitted he made a mistake in the original trial by incorrectly pointing out the position of the lens in a photograph.
He was grilled by defence counsel Michael Reed, QC, as to how such a mistake could ever be made.
Mr Reed challenged Mr Weir over the credibility of his evidence and put it to him that he deliberately misled the jury.
Mr Weir replied he did not deliberately mislead the jury and that he was being truthful in his evidence.
The court was told Mr Weir did not preserve carpet on which footprints, which may have been made by the killer, were found.
Mr Weir took part in recording the length of footprints found in the house during an examination using luminol. The Crown says the footprints were David Bain's.
However, Mr Weir told the defence that the carpet was not kept. Mr Reed told the court the Bain house was burnt down approximately 14 days after the killings and Mr Weir accepted that meant the defence could not do their own tests on the footprints.
Mr Weir also gave details of his examination of Stephen Bain's bedroom. He said many items were covered in blood, including a pair of Nike running shoes, one of which had "D Bain" written inside it.
The shoes were taken as exhibits, along with other pairs of shoes and items of clothing.
Key to gun found in father's van
The court was told a key to the trigger lock on David Bain's .22 rifle was found in his father's Commer van.
Under cross-examination, Mr Weir told the defence that a set of four keys was found in a pocket of an anorak inside Robin Bain's van.
Mr Weir said he understood that one of the keys fitted the trigger lock to the gun, but he did not check to see if the key fitted.
The trial heard earlier that David Bain told police he was the only one who knew where the keys to the trigger lock were kept.