Here's a list of why I think Scott Watson should be retried, I'm sure there others I've overlooked. Feel welcome to send details.
1/ Rozz McNeilly a shift Manager of the Furneaux Lodge no longer positively identifies Watson as being with Olivia in the bar. She says she was tricked by police in identifying Watson and realised this later.
2/ Guy Wallace no longer positively identifies taking Watson and the couple to board a boat together in the early hours of new year's day. Guy says that he was tricked or mistaken in his belief the man with the couple was Watson. McNeilly and Wallace no longer put the couple together with Watson, and even more importantly together going onto Watson's yacht.
3/ A couple are now identified (I don't know if they gave evidence at the trial) who were rafted to Watson's boat the Blade and others when he came aboard in the small hours looking to party and proposed to the woman's partner that she might spend some time with him. The vessel was The Blanco, at the this time according to the Crown's sequence of events, Olivia and Ben were either dead or alive on The Blade when Watson anticipated going with the woman on the Blanco back to The Blade where the couple were. This is a major and serious flaw in the Crown case. I don't know whether it has been touched on before, but when added to evidence now favouring Watson it points to him being innocent.
4/The mystery ketch of this case may now have been identified as the Alliance, however there are other, what would be new witnesses, that saw 2 ketches at the same time (one being the Alliance) soon after the disappearances - providing the possibility that the mystery ketch seen at the same time as the Alliance had the couple on board or that they had been on board some time earlier. The second unnamed ketch was seen by several witnesses whose recollections appear clear and bring another new dimension to the case that was not heard at the trial.
5/A witness saw a person on a ketch (not the Alliance), after the couple's disappearance, that he believes was Olivia. This wasn't a drunk person at the Lodge, but someone out on the water following new year's eve. His evidence is also new, and material.
6/ 2 hairs lifted from a blanket from the Blade and said to belong to Olivia are now identified as being from the same hereditary line as Olivia's mother. In other words they could have belonged to either Olivia or her sister. Whilst they were not found on a first thorough search in the Laboratory, the 2 hairs were found in a subsequent search on the same day that a hair brush belonging to Olivia's sister was delivered to the lab. The 2 hairs were later found to be contaminated from other contact. There is now evidence to say that the contamination could have happened by the brush being used by the 2 sisters, probably not an unusual event in a household. It's important to note that a/ there was absolutely no other evidence found on the blanket, or indeed the Blade, which linked to the missing couple, and b/ that I do not know the laboratory practice techniques employed reached an international standard that ensured no possibility of cross contamination of the hairs within the lab.
7/ A witness who claimed Scott Watson 'confessed' to murdering the couple and who gave disgusting details of the crime has recanted. The NZ police are now unable to find this witness, however his evidence still stands like that of other witnesses above as indicting Watson when that no longer is the case.
8/ A recent book by Ian Wishart, which I apparently 'fisked,' what ever that term means, exposed (possibly inadvertently by IW) that identifications of Watson and a second person who may have been in contact with the couple in the bar are horribly compromised. This is supported by what Wallace and McNeilly now say. Along with another witness who saw Watson after the couple's disappearance when Watson was allegedly trying to hide and disguise his boat, Watson waved out to him. It must be remembered that Watson never denied being in the bar, there is no suggestion he had disguised himself in anyway, while in fact there are clear indications he drew attention to himself as did many others that night in a confusing flux.
9/ Also, thanks to Wishart's book Elementary, we now know that Watson had intended to paint his boat long before he eventually did after the couples disappearance. What is also apparent, and which wasn't appreciated by myself before reading Elementary, is that Watson was well known to police in the Sounds, and consequently therefore to the locals there. None of those locals identified Watson at the Bar.
10/ 'Secret tapes' exposed by Wishart into conversations held in the Watson household show the family did not believe that the couple had disappeared and thought they would turn up again. The tapes also show that a PI hired by the family asked questions that on the face it looked like they may have been questions the police were interested in knowing the answers too. The tapes, which arguably should not have been revealed by Wishart are now material to the fact that the Watson family firmly believed the couple were not dead. They did not, as has been implied, look to cover for Watson but certainly were concerned about the attention he was receiving as a suspect.
Some of the material above was included in the application by Watson for exercise of the Royal Prerogative of Mercy. When that application was turned down, and the findings made public it was revealed that the investigator of the application looked at all the points favouring Watson individually before dismissing them - presumably in doing so relying on other points of the application to do so. So where the supporting evidence may have failed to cross threshold of bringing doubt upon Watson's conviction, it was seen as supporting evidence in refusing the application.That reviewer, Kristy McDonald, never looked at the points in continuity, that is a Miscarriage of Justice. It is a requirement in practice for items of pivotal importance in a case to be looked at individually and then collectively. What surrounds weak or strong evidence is to be viewed as to whether it adds or reduces weight to the evidence. That was never done in a way consistent with due process and fairness, let alone using a word never used in the finding, with Mercy.
I think even a pessimist sold on Watson's guilt can acknowledge that points above (including others that I may have missed) are matters for a Jury to decide the individual and collective weight and therefore should have been referred to the NZ Court of Appeal as the legislation allows. The Watson conviction is weakened on many fronts by new material that stands alone, and in sequence, in a manner which undermines the validity of his conviction. Some single points appear to tip the balance in Watson's favour as unfairly standing convicted, but it is the overall continuity of a number of points which fully turn the tide against the convictions to a point of requiring a retrial.