To get its not guilty verdicts, the David Bain defence team needed to provide grounds for reasonable doubt and a convincing villain.
They needed to make the trial about David's father Robin.
They needed to make him appear potentially suicidal, and they had to make him strong enough to win the fight to the death with his 14-year-old son, Stephen, and physically capable of shooting himself in the head with a rifle.
The Crown said the suicide was too difficult: that he would not have been able to juggle the heavy .22 calibre rifle, with the silencer on the end, and hold it at the improbable angle required to shoot himself in the temple.
But there was a day when all that changed. Wednesday, April 8.
On that day, about a month into the three-month High Court hearing in Christchurch, the trial came alive.
The defence said the suicide was viable and produced seven photographs to show how Robin could have killed himself with the rifle.
Suddenly, suicide was at least a possibility and Robin was back in the picture.
The experts would argue the details, and disagree for weeks.
For some, the rifle was held close to the head, and for others it was more distant.
Photographs were examined minutely. Every blemish on the skin of Robin Bain seemed to be on trial there for a time.
And the bottom line is that some of the highly qualified experts who came along to High Court No 1 to give evidence had to be just plain wrong.
The defence spent weeks establishing the black and bleak world view of school principal Robin Bain, struggling with his health, his job, his marriage.
His life was a mess whether living in an old Commer van near Taieri Beach School south of Dunedin during the week, or living in a caravan at the family home at Every Street, in the city, at the weekends.
His life was coming apart, the defence said.
And on the night before the killings it all came to a ghastly head with a family meeting and presumably the revelation that Robin had been sexually abusing his 18-year-old daughter Laniet for years.
It seems that so many of the Bain family had to die because they knew something.
This strange, dysfunctional family had secrets and their house with its eccentric lines, slumps, faded and peeling paint, looks rather like a metaphor for the oddities within.
Robin was painted as being at the edge of reason, disorganised, hopeless, ill and frail -- a walking cadaver one witness said.
Margaret was a mother who wanted to bulldoze the place and build again, but not a house, a retreat. She was a mother who had new age spiritual beliefs, and once decided that she was going to go to bed for six weeks.
Arawa, aged 19, seems to have been the one who kept the household ticking over.
Laniet no longer lived there but stayed that night. She had been working in the sex industry but had given it up. Portrayed by the Crown as a flake, a girl who claimed to have had three children by different fathers and an abortion by the age of 12-and-a-half.
The defence said she was in an incestuous relationship with her father, and she mentioned that time and again -- not just to her friends, her workmates, but even to the grocer who lived across the road from her flat.
Stephen was a fit, strong boy and he undid the killer's plan.
How could a teenage boy be such a danger? By waking up, probably.
When the killing began in the morning, Laniet Bain was probably the first to be shot.
In fact, she seems to have been at the centre of the maelstrom that engulfed the family in that pre-dawn hour on June 20, 1994, at number 65 in the street with the oddly inappropriate name, Every Street.
Then the killer shot Margaret, killed in her bed.
There was only a curtain between her bedroom and Stephen's room and it seems like the sound must have woken the boy.
He got up. He was moving when the killer entered through the curtain and he put up a fight that upset all the plans for the quiet dispatch of the family.
The first shot went through Stephen's raised hand and glanced off his head. There was blood spurting and the boy fought for his life.
He scratched, struggled, and had to be strangled into submission with his own t-shirt twisted around his neck. It seems he was still conscious as the killer took the rifle and fired the final head shot that killed him. He had his hand up to the rifle even then.
For reasonable doubt, the jury had to accept that Robin Bain was capable of getting into this fight and winning.
The Crown said it could not be Robin, because he was too small and not strong enough. Stephen was 55kg and Robin was 72kg. But Robin's brother, Michael Bain, said last time he saw Robin, he was able to pick up a very heavy bag that he couldn't lift himself.
The defence made the point that Stephen had been shot in the head and probably through the hand as the brutal encounter began.
He may have been stunned, shocked, in pain and one-handed. Could that have been enough to give the older man the advantage? But it begs the question: why did the killer wear gloves -- white opera gloves that belonged to David and were found covered in blood in Stephen's room?
What was Robin's plan if he needed to conceal his fingerprints? Before he supposedly made the decision to kill himself, can it be that he was hoping to frame David for the murders? If it was only David who had any reason to wear gloves, what was the defence's reply?
It was simply this: Don't try to make up a rational explanation for someone who was acting irrationally.
The defence had to contrast the two men, forcefully and in detail.
It said the elder man was suicidal, depressed, revealed as a sex abuser, while his son David loved his family and had everything to live for.
David was portrayed as jovial, convivial right up to the day before the murders -- a man who had made a music CD the week before and might have had a career ahead as an opera singer.
The difference too was that David Bain was right there in court looking calm, normal, rational.
He was confronted by the crime's ghastly images on the court's computer screens as much as anyone else, and looked away.
He was seen every day walking between the defence team's lodgings nearby and the Court House.
When he arrived at the courts on the day of the defence closing by Michael Reed QC, a group at the doors clapped and wished him luck.
On one Saturday early in the trial, he could be seen with a coffee in hand, taking a punt ride on the Avon River near the courts.
It was done without media attention, except for a court reporter waiting at a bus stop. The normality of it was stunning.
The defence played upon his presence with skill, with Mr Reed's very last exhortation to the jury: "Put David out of his misery, return him to freedom with a not guilty verdict on all charges."
