What makes the Crewe and Bain cases similar.

One striking similarity is the 'golden bullet' evidence. The evidence for some reason which is not originally available but which 'happens' along to connect a picture for the case under investigation and drive it toward an unsound conviction.

Firstly take a look at the protagonists, David and Arthur. What they share in common is that they were 'clean skins' with a healthy respect for the law and a naivety about the role of the police, the type in fact to co-operate in their own demise. In the beginning both men freely answered questions, often without regard for the consequence of their answers and how those answers might be used against them. They were both genuine men who thought highly of the system and respected that the law and justice would prevail. Though I'm sure if they were asked now they would acknowledged that they had lost faith in the system long before the good ship justice was righted for each man individually. I'm sure they will admit under pressure to expecting to never fully recover from a situation that stole so much from them, so much that can never be replaced or compensated for.

But back to the golden bullets, to name the golden bullets in the Crewe case was the discovery of cartridge case that was missed in the first searches and when found was ultimately proven not to have even been manufactured at the time of the Crewe deaths. And of course the axle with a 'positive' match for parts found on Arthur's farm. Golden bullets, breakthroughs of injustice by the men tasked to uphold the law.
When pressure mounted on the evidence after the trial, suddenly material was dumped at the Whitford Tip as would also happen with evidence destroyed by the Police in the Bain case.

And similarly with David. A small room searched for days, then several nights later, an officer not tasked with the duty of searching, returning to that room virtually after hours and 'finding' a lens somehow apparently 'missed' by his colleagues. Then the frame of the glasses found in David's room and to span 13 years an officer revealing for the first time that David had asked for those glasses on the morning of the murders (despite they being of no use to anyone because they were without lens) but the officer had not wanted to mention the 'truth' earlier because he didn't want to criticised. The quality of truth rendered to the reaction possibly made to the speaker, rather to unequivocal honesty regardless of any impression, favour or disfavour.
But these are only a starting point to build on those others have made which show these two cases to be chillingly similar. I used the words 'golden bullet' taken from today's Herald where an ex FBI investigator comments about the conviction of Amanda Cox where he says 'any time that you go back to a crime scene six weeks after the event, and suddenly come up with a piece of evidence that is effectively the "Golden Bullet," that is suspicious. At best it is contaminated. In the UK or the US it would never have been admitted as evidence.' Of course in NZ, as in the case of David and Arthur, the 'golden bullets' once discovered were 'put in context' by the Judiciary who allowed the Crown to carry on and there is probably the key similarity between the two, even with things wrong with substantially important evidence, Miscarriages of Justice were allowed to 'carry on.' Even today idiots like Mike Stockdale, cobble together apparently un-discredited evidence from discredited witnesses, from a discredited investigation to carry on persecution. That is what will stop when an OIC of an investigation or an Area Commander or a Commissioner of Police, or Minister of Police will find abhorrent, poison and toxic anything with a hint or a smell of being a 'golden bullet,' anything found which was 'apparently' missed earlier, or not mentioned for fear the witness might be criticised. When those same men or women at the top rightly act with cynicism and not excitement or satisfaction that at last a 'breakthrough' is made on an important case.