Forget the forensics (much of which would later be discredited) for a moment. Park any references to blood, bullet fragments and fingerprints on the rifle. Let's look instead at personality.
Robin Bain. School principal. Married father of two sons and two daughters. He was a man who was broken in almost every sense.
Estranged from his wife, he lived in an advanced state of squalor. His career was stalled; he was no longer the respected leader he had once been. He looked, some would say, like a walking cadaver. He had undergone a monstrous personality change, prone now to fits of anger and frustration when he was once nothing but calm.
This is a picture of a man removed from social normalcy, somebody who had lost his own sense of self and, in so doing, abandoned all responsibility to his charges. If he was already on the brink, the threatened revelation to their family by his prostitute daughter that he had been sexually abusing her for years was surely the denouement.
Was all that sufficient motive for a multiple murder and suicide? Campaigner Joe Karam indicates that it's certainly a major contributing factor.
In his book Trial By Ambush: the Prosecutions of David Bain, Karam unequivocally fingers the Dunedin school principal for the murders of his wife and three of their children before shooting himself.
That is no surprise: Karam has long championed sole survivor, son David Bain, as innocent of the five counts of murder for which he served 13 years in prison, before being found not guilty at retrial. But in this latest book on the murders, Karam articulates in meticulous detail the case against the man who he sees as the true killer.
To back his argument, he explores the prosecution testimony, much of which was later exposed as flawed, then reaches for an academic and psychological explanation.
By many accounts, Robin Bain was ideally suited for committing murder/suicide. Not long before the wintry 1994 killings, he sought stress leave from his post as Taieri Beach School principal. His life was by then out of control. A true illustration of this lies in the photographic section of the book: a picture of the rusted Commer van, his weekday home at the school for three years. It is a portrait of decrepitude.
Adjacent is a photo of the 20 bullet shells found in the caravan in which he camped at the weekends at the family home, the scene of the killings. Above is a picture of his bed in that caravan, on which is the reading material Death at the Dolphin and Agatha Christie's Death Comes as the End.
Who knows what went on in his school - 9-year-old pupils wrote graphic and inappropriate stories of violence and killings. The week before the Bain murders, some were printed in the school newsletter. To his colleagues: "Robin had lost touch with reality."
Consider, too, what fellow principal Malin Stone encountered when he went to Taieri Beach School to help out on the day after the killings. Robin's classroom was "a shambles".
The pupils - 10- and 11-year-olds - did not know where their reading or maths material was and their literacy level was below average.
The scene was chaotic. Ditto Robin's office: mess galore - piles and piles of it. Robin wasn't paying much attention to his personal hygiene, either. But he did put some of his affairs in order in his final days.
He tried to enlist the services of a relieving teacher (she was unable to help as she was contracted elsewhere). He sought a final reading on the electricity bill at the school house in his name. And he insisted on settling daughter Laniet's account at the Dunedin dairy she frequented. This was wholly out of character.
The second trial would hear that Laniet had resolved to reveal to her family that same weekend her prostitute lifestyle and alleged incestuous relationship with her father.
Not everybody noticed Robin's deterioration. Some Crown witnesses said he was a caring and diligent teacher, much liked by parents and children.
This is not disputed, Karam says. "However, it does not detract from the factual matters illustrating the dramatic degeneration of aspects of his life."
The Bain case looks like familicide-suicide, he indicates. "Although there are some extremely rare cases where such familicide is committed by the mother or some other member of the family, more than 95 per cent are committed by the father."
The profile of David, 22, does not appear to qualify him to be among the remaining 5 per cent. According to Karam: "Only about 1 per cent of cases of familicide are committed by a child of the family, and when they are committed by an adult son he almost always commits suicide, too.
"In cases where sons killed both parents, the research indicates that the perpetrator is always either severely abused, suffering from severe mental disorders (usually psychotic) or psychopathic. There are no identified cases where the son exhibits none of these pathologies and does not commit suicide."
Indeed, David's psychological profile is presented as healthy. Psychiatrist Dr Philip Brinded, who visited David in jail repeatedly, told the retrial that he never saw any psychopathic tendencies or characteristics in him.
Ignominy: That's what Karam reckons was the final straw. "There is usually a specific event that is the final straw triggering the familicide, one that leads in the perpetrator's mind to ignominy: a terminal public shame, mortification and self-disgust ... It is always one over which the perpetrator has little control, and is going to publicly expose his failure."
Will the debate over who did it ever end? Last week, in a special interview with the Herald on Sunday ahead of the book's publication, Karam said he had not wanted to write it. He was moved to do so simply to "dispel the myths" that had emerged after the second trial.
After the Privy Council quashed David's original conviction, many commentators were adamant there should be a retrial on the basis that a jury verdict was needed to put the matter to rest once and for all.
But when David was found not guilty, said Karam, some of those same commentators started to question the jury's decision. It seemed they didn't like that verdict, either.