This evidence was originally suppressed “until completion of the re-trial” as, per Wilson J,
The probative value of the disputed sounds is very modest, but the risk of prejudice resulting from their introduction into the trial is very great. There is more than a minor imbalance; the scales come down firmly on the side of exclusion of the evidence. Even if the disputed sounds were admissible under s 7, they should plainly be excluded under s 8. [of the Evidence Act 2006]
Due to this decision the original suppression case has now been made public and was also released this afternoon. Now you can read David Cullen Bain v The Queen  NZSC 16 and find out why the court decided on 6 March 2009 that the disputed evidence (the alleged "I shot the prick" part of the 111 call) would be excluded and that part of the call would be excised. (Full transcripts of the various interpretations of David Bain's 111 call are included in the reported decision.)
Extract from the decision of Supreme Court of New Zealand on the appeal to suppress the evidence, per Elias CJ and Blanchard J at paragraphs 3, 4 and 5:
... The presence of the disputed admission was first found by Detective Ward, when he reviewed the recording, in preparation for the retrial, in July 2007. At that time he listened to the recording at a commercial sound studio in Dunedin. Mr Dempsey, the ambulance officer who took the call, had not heard the disputed words and did not suggest their inclusion in the transcript originally prepared in 1994. In October 2007 he was asked to recheck the recording after being told of the words which had been discovered. In listening to the recording with that knowledge, he heard the words “I shot the prick I shot” and was “stunned that I hadn’t heard the words previously”.
Because of the discovery, the recording was sent for analysis to the United Kingdom to forensic consultants, expert in analysing recordings of speech. It was also analysed by experts for the defence. There is very little difference between the experts as to their findings. The opinions constitute evidence extrinsic to the recording itself upon which the decision to admit the recording was based.
Although it is necessary to refer to the forensic opinions at some length later in these reasons, they may be briefly summarised for present purposes. None of the experts is able to say that the sounds relied upon in the recording are words, rather than meaningless exhalation of breath. If they are words, none of the experts is able to say that they amount to the words the Crown wishes to rely upon as evidence. Some consider such words can be heard in the recording, with effort. But all experts caution as to the dangers of hearing something that may not in fact be there, because of accident in arrangements of sounds. ...
Three reasons weighed principally with the Court of Appeal in concluding that the evidence of the disputed words on the recording should be admitted. They were the fact that the “hypothesis” was “open” on the expert evidence; the fact that the appellant spoke on an exhaled breath without vibration of the vocal folds when giving his telephone number; and the “contextual sense” of the sentence, which left it open to the jury to decline to accept that the sounds had been made by random movements of the tongue and lips in an exhaled breath. ...
... The prejudicial effect on the proceeding could be profound. The jury would, as Mr Raftery acknowledged, be entitled to find the accused guilty simply on the basis of an inculpatory statement unable to be proved to the satisfaction of experts or, in their estimation, of lay people. ...
... For these reasons, we consider that the disputed sounds are not admissible. The risks of jury speculation as to the content of the sounds, and the risk of the contentions put forward being available to them, make it necessary to excise the portion of the recording.
JJ McGrath, Wilson and Gault's judgments are shorter and add slightly different angles, all of them agreeing with Elias CJ and Blanchard J, that jurors may not be able to make the necessary complex and extremely important distinctions and that they should not be given the chance to get it wrong.
Notably none of the justices appear to give any consideration to section 14 of the New Zealand Bill of Rights Act 1990 as they are required to,
Freedom of Expression - Everyone has the right to freedom of expression, including the freedom to seek, receive, and impart information and opinions of any kind in any form.
As such, the interests of justice must be weighed against the right to expression "and only where the Court's capacity to ensure justice is significantly imperilled will the right of citizens and the media to seek, receive and impart information be curtailed." (Thomas J in Police v O'Connor  1 NZLR 87, 99) In deciding to grant a suppression order the court must take into consideration the effect of doing so on freedom of expression, alongside its affronts to the principle of openness, and engage in the weighing Thomas J referred to - especially when the court is the highest court in the land, cannot be appealed from and is overturning a lower court's decision. I cannot find where they considered it, let's hope they thought about it even though they appear to not have recorded doing so.
The fact that the previous courts had not allowed the appeal and the Supreme Court did, will undoubtedly open up the arguments around the abolition of appeals to the Privy Council. If you want to see the judgements and compare the reasoning of the lower courts that originally allowed the appeal - you'll want to start with The Queen v David Cullen Bain  NZCA 1 and work your way back from the Court of Appeal to the High Court [the direct link to the pdf of this case won't work so go here and click on the '30 January 2009' decision entitled "CA 571/2008 (PDF)"].
Personally I tend to lean towards the Court of Appeal's thinking on this one, that while the nuances are complex and very important to grasp, managing this evidence would not have been impossible; starting at paragraph 256,
... As to prejudice, the primary risk is that the jury may wrongly construe the disputed sounds as an inculpatory sentence – in other words, may simply get the facts wrong. But risks of this sort – that the trier of fact may get the facts wrong – are an inescapable part of the trial process and do not in themselves usually represent the sort of prejudicial effect which warrants evidence exclusion. It is, of course, the responsibility of the judge to guard against obvious risk (and particularly one that will be more apparent to a professional judge than lay jurors) of misunderstanding. In this case, there is an obvious risk, namely suggestibility, which must be addressed. But providing this happens, we see no reason why the evidence should not be admitted.
As the Judge noted, it is well settled that the interpretation of an item of real evidence, such as a tape-recording, is a jury question: see for example R v Wickramasinghe (1992) 8 CRNZ 478 at 481 (CA) and R v Taylor  1 NZLR 647 at 650 – 651 (CA). The Judge took the view, with which we agree, that a transcript is not required, given the short length of the conversation (about a minute).
We think it would be best if the jury first heard the tape without being primed, except perhaps with a request that they listen to it carefully and possibly advice (as recommended by Professor French) that they will hear some speech produced on breath. If they initially do not hear the disputed sounds as an inculpatory sentence (which we think is likely given past history [no one noticed this sentence during the first case]) but, once primed, subsequently do hear the disputed sounds in this way, this should provide a graphic indication of the power of suggestion.
The Judge concluded that after the tape has been played to the jury “unprimed”, expert evidence should be received concerning the interpretation of the disputed sounds. We agree.
We have no doubt that in his summing up the Judge will warn the jury of the dangers of suggestibility. ...
... it would be quite extraordinary for this Court (or the Judge) to deny the jury the opportunity to listen in full to what the Crown can credibly claim is a recording of the account given by the appellant, within 25 minutes or so of the completion of his paper round, of what he found when he returned to the house.
How to Find the Reported Judicial Decision on the David Bain Re-Trial