A computer expert has told a jury he cannot say exactly what time the Bain computer was turned on the morning five members of the family were killed and that some of his work involved assumptions and guesswork.
Maarten Kleintjes, national manager of the police electronic crime laboratory, was giving evidence for the Crown at the retrial of David Bain in the High Court at Christchurch on Friday.
The Crown says David Bain, 36, killed his parents Robin and Margaret and siblings Arawa, Laniet and Stephen at the family's house in Dunedin on 20 June 1994.
The defence says Robin Bain killed the family present in the house before shooting himself.
The Bain family's computer is a key part of the case, as a message saying: "Sorry you are the only one who deserved to stay" had been typed on it the morning that five members of the family were found dead in the Every Street home.
Minutes and seconds are under scrutiny as Mr Kleintjes gave evidence about the time the computer was turned on.
The Crown says David Bain killed his family, turned on the computer and typed the message to frame his father Robin.
But the defence says at the time the computer was turned on David Bain was still on his paper round.
The times are important because David Bain was seen outside his house around the time the Crown says the computer was switched on. If that is so, he may not have been the one who typed the message, which the defence says Robin Bain actually did before killing himself.
On Thursday, the jury heard from Martin Cox, a computer expert who said he estimated that the computer was switched on at 6.44am.
But on Friday, Mr Kleintjes told the court there were "numerous variables" which could change that assessment. He said despite complex analysis, he had used guesswork to help in his calculations.
The watch used in the initial testing of the computer provides many variables alone: it was not only inaccurate, but it only measured time in five-minute increments and its rectangular shape meant it could be easily misread if viewed on certain angles, the court was told.
Mr Kleintjes gave evidence about the internal workings of the Bain's computer and explained the way it recorded times and dates and how a clone was taken of it to do his testing.
But after a complex, scientific testimony, Mr Kleintjes told Crown prosecutor Kieran Raftery that he could not say with any certainty what time the computer had been switched on the morning of the killings.
Defence lawyer Michael Reed, QC, challenged his evidence, telling the court that expert witnesses should not be allowed to guess.
He said the range of times Mr Kleintjes put forward regarding the time the computer was switched on was impossible.
The trial continues on Monday.