KEY POINTS:
Let us presume David Bain was innocent, as we must now that his conviction is quashed. That means the callow 22-year-old, who turned into the calm, collected man we met this week, really did come in from his paper run that morning to find every member of his family slaughtered.
Maybe after trauma of that enormity nothing can hurt you, not even the horror of being judged the cause of the devastation done to you, or the next dozen years in the fearful, noisy, stinking confines of a prison.
As far as we can tell Bain handled prison very well.
Reportedly, he worked and studied, keeping to himself, maintaining his innocence but not visibly angry about it, not festering with resentment as I would be if life had dealt me such injustice.
The Privy Council decision has prompted comparisons this week with Arthur Allan Thomas, but Thomas didn't lose his family. He was not a victim of the crime he was accused of committing.
Nobody except David Bain knows whether he really is innocent, though everybody is expected to have a verdict on it.
We have become a national jury for a case that long ago outgrew a courtroom. We know far more about that disturbed family than the real jury did, but I wonder whether we know enough.
There is only one person alive who might know with any certainty why someone massacred them, and why he was "the only one who deserved to stay".
I have read Joe Karam's account: the estranged parents; the outcast father, depressed; an incestuous relationship with his daughter, a prostitute, who had just come back home.
But David Bain plays strangely little part in the story. What was his attitude to the others and his role in the family's tensions? Why did he deserve to stay?
We know nothing about what happened the night before in that cluttered, ramshackle house that might have prompted someone to rise before dawn, take a gun and go from room to room.
It is easy to imagine a motive for the father; less so, but not impossible, for a son. Too easy, Joe Karam would agree. As an amateur sleuth he learned the mental discipline of a detective trained to follow evidence, not theory.
Theories filter your vision of what you find and can blind you to the obvious. Even detectives alert to the danger succumb to it sometimes. So do judges.
Reading the Privy Council decision this week I was left wondering why Robin Bain changed his socks. A bloody sockprint in the hall of the house was one of the fragments of "fresh" evidence that led the Lords to recommend a retrial.
At the original trial defence lawyers did not dispute that David Bain had made the sockprint.
But the day after the verdict Karam measured his feet and found they were 2cm longer than the heel to toe print. His father's feet were 1cm shorter and conceivably could have left it.
The Privy Council found this significant because the socks Robin Bain was wearing when found dead were not blood-stained and if he changed his socks he conceivably changed other garments as well.
The idea that someone would pad around the house killing people and change into clean clothes for his suicide is, the Lords acknowledge, not something a normal and rational person would have done.
"But the jury [in a retrial]", they decided, "might conclude that whoever committed these killings was not acting normally and rationally."
I remember the first time I covered a murder trial. What struck me was the normality of the young man who was found guilty.
He was unlike the usual customers of the criminal courts. He hadn't been in trouble before, for one thing.
He was neat and tidy and thoughtful-looking and seemed detached from the proceedings about him.
As the case unfolded the courtroom was united in an overwhelming sense of tragedy. I forget the details now but it was obvious to all present that an unfortunate conjunction of circumstances had made this normal, even "nice" young man commit the worst of all crimes.
Everyone watching hoped the crime could be reduced to manslaughter, but he knew what he did could cause death and didn't care if it did. In law that's murder.
He wasn't really a danger to society. Maybe in the same circumstances he would do the same thing again, but even the prosecution agreed, as I recall, that the same conjunction of circumstances would not happen to him again.
It was not the last murder trial I saw of that kind.
Murder can happen for reasons so intensely personal and private that the accused person wants to keep them from everyone - investigators, defence lawyers, prison counsellors, even dogged supporters in those cases that are open to different verdicts and fascinate us forever.
