Judge Ian Binnie identified some highly significant mistakes made by the police in  the course of their investigation into the killings at Every Street. These are covered in pages 155 to 192 of his report into David’s claim for compensation. The most egregious mistakes included:

Failure to investigate allegations of incest: the police failed to follow up on concerns about Robin Bain’s mental health or on Dean Cottle’s allegations of incest by Robin Bain (see below for more detail);

Destruction of evidence: the police allowed the house where the killings occurred to be burnt down three weeks after the deaths which meant crucial evidence was destroyed; they also ordered the destruction of additional evidence about 12 months after the trial;

Misleading the jury:  The police:
a) told the jury the spectacles found on the floor of the house belonged to David after their expert witness changed his evidence and said they belonged to David’s mother;
b) gave inaccurate information about where the left lens of the spectacles was found;
c) gave the jury a definitive time about when the family computer was switched on when the evidence did not support this;
d) failed to tell the jury they had checked a key witness’s clock confirming the time David returned to the house after his paper run.

Failure to investigate allegations of incest

The most egregious mistake, with devastating consequences, was the police failure to follow-up on the allegations made by Dean Cottle that Laniet was being sexually abused by her father. Prior to arresting David, the police were well aware that Robin Bain had been under stress and was potentially unstable. They knew about the marital discord between David’s parents and “the curious activities at the school over which Robin Bain presided”. But they eliminated Robin Bain as a possible suspect two days into their investigation.

Even after Cottle made his allegations of sexual abuse, the police refused to investigate this issue any further.  As a result, the judge’s decision to reject Cottle’s testimony as unreliable was almost inevitable – because there was no corroborating evidence. The problem was the police never bothered to look for any.   On the witness stand, senior detective Sgt Doyle said the police did not investigate allegations of sexual abuse against David’s father was because “this was a homicide investigation, not an incest investigation” (para 538).

Judge Binnie criticised the police for this failure. He wrote:

The lack of interest in a possible motive for Robin is all the more surprising as the Police never did uncover a motive for David Bain other than a minor disagreement with Robin on 19 June (the day before the killings) as to whether Robin would take the family chainsaw to Taieri. This is hardly a plausible motive for David Bain to kill five people in the absence of evidence (of which there was none) of a serious mental disorder” (para 539).

Ian Binnie summarised his conclusions as follows:

“Having regard to the terms of the Cabinet’s ‘extraordinary circumstances discretion’ set out in the Minister’s letter to me of November 10, 2011, it is my opinion that the egregious errors of the Dunedin Police that led directly to the wrongful conviction make it in the interest of justice that compensation be paid” (para 27).