You don’t need me to point out that the law loves its metaphors. Most of all, the metaphor of scales: decisions are often described as balancing exercises. Justice with her scales. So it is with s 30(2)(b) of our Evidence Act 2006.
A decision whether to exclude improperly obtained evidence requires careful and clear reasoning, for a refusal to take account of credible relevant evidence is a serious matter. Section 30(3) lists matters to which the judge may have regard, although this is not an exhaustive list. But the message is that particularity is needed when explaining whether improperly obtained evidence should be excluded.
One imagines, therefore, that various considerations fall on one side or the other of the metaphorical balance. Depending on the circumstances, they will be given varying weights, on the side of the balance that is appropriate.
The need for judicial decisions to be predictable, and not arbitrary, reflects the need for litigants to be able to anticipate the outcome of their arguments. The balancing exercise must be as consistent as possible between cases. Some factors will always be on one side of the balance (favouring admission of the evidence) while others will always be on the other (favouring exclusion).
All well and good, in theory. But in practice things have got a bit muddled. There has been confusion over whether the seriousness of the alleged offending is always a matter that weighs in favour, to varying degrees, of admission of improperly obtained evidence. You would expect that the more serious the alleged offending, the more likely it is that evidence will be admissible notwithstanding that it was improperly obtained.
But there is a limit to that. It has been said that seriousness of the alleged offending “cuts both ways”. This introduces a sword (or perhaps a pruning saw) metaphor to combine with the scales metaphor. Accordingly, it is said that seriousness favours admission of the evidence, but where the seriousness is high it weighs in favour of exclusion, because in serious cases there is a heightened public interest in having law enforcement officials obey the law.
Let’s examine that. Is it the seriousness of the offending that weighs in favour of excluding the evidence, or is it the heightened public interest in having enforcement officials obey the law? Is the public interest in having law enforcement officials obey the law greater, the more serious the alleged offending? Isn’t official obedience to the law just as important in ordinary cases? The more technical an offence, the stricter should be compliance with the law by the authorities, surely. Why should (and here’s another metaphor) the pot be allowed to call the kettle black?
The idea that “there’s more at stake for the defendant” when the alleged offending is serious has been offered as a justification for recognising a heightened public interest in official obedience of the law. But, isn’t the public interest in bringing alleged offenders to trial greater, the more serious the allegation? Why is the defendant’s interest in having officials obey the law greater when the defendant was allegedly disobeying the law in a serious way?
The balancing model demonstrates that a "cuts both ways" approach amounts to double counting. It is one thing to remove a weight from one side of the scales, and quite another to then put that same weight on the other side.
Given that it is always nice to have enforcement officials obey the law, there must be some instinctive resistance to accentuating that desirability in cases of alleged serious offending. This might explain why senior judges can differ in the outcomes of their balancing exercises in a given case.
For example, our Supreme Court split 3-2 on the admissibility of improperly obtained evidence in a case this year. It currently (as far as I am aware) is subject to suppression orders, so I just call it R v [Name suppressed]  NZSC 16 (5 March 2020), and I avoid discussing its facts. The majority judgment of Winkelmann CJ, O’Regan and Brown JJ, includes the following, which is an account of the law which I summarised above:
“... As has been noted on many previous occasions, the seriousness of the offending is “apt to cut both ways” [Footnote: Hamed v R  NZSC 101,  2 NZLR 305, at  and  per Tipping J. See also R v Chetty  NZSC 68,  1 NZLR 26 at ; and Underwood v R  NZCA 312,  2 NZLR 433 at –.] If the offending is serious, that favours admission. However, if the offending is serious and the nature of the impropriety raises issues as to the quality of the evidence, that will tend to favour exclusion. That consideration does not apply in this case. But even where the nature of the impropriety does not impugn the quality of the evidence, there remains public interest in the careful and lawful investigation of offences, particularly serious offences. [Footnote: Underwood at –.] As Tipping J said in Hamed, citing the Supreme Court of Canada in R v Grant 2009 SCC 32,  2 SCR 353 at :
... while the public has a heightened interest in seeing a determination on the merits where the offence charged is serious, it also has a vital interest in having a justice system that is above reproach, particularly where the penal stakes for the accused are high.” 
I think this makes the mistake of treating the decision criterion (the need for an effective and credible justice system – s 30(2)(b)) as if it were a balancing matter. The decision criterion is a constant, applicable to every admissibility decision under this section. It is always, and not just in cases of alleged serious offending, necessary to have a justice system that is beyond reproach. The balancing matters, in contrast, some of which are set out in s 30(3), vary in significance and some may not be relevant at all in the circumstances of a given case.
In dissent, Glazebrook J – if I may summarise broadly - thought it was significant that alternative lawful means of obtaining the evidence had been available (so any impropriety was not particularly serious), and that there were sufficient lawfully obtained grounds for the issuing of the challenged search warrant, so the evidence should have been admissible. No suggestion here of a heightened public expectation that officials should obey the law.
Ellen France J dissented – again I summarise broadly, and paraphrase - in the application of the balancing exercise, giving greater emphasis than had the majority to the nature of the evidence obtained and the seriousness of the offending.
So, while the majority included what I might call the ‘reverse cut’ (a cricketing metaphor?) in carrying out the balancing exercise, the minority judges did not. Its presence or absence does not account for the judicial differences in conclusion, but it would take a bold person to deny that it played a part.
We could avoid any complicated arguing over whether the seriousness of alleged offending can weigh in favour of exclusion of improperly obtained evidence by simply recognising that sometimes official impropriety is so bad that it will always lead to the exclusion of evidence obtained as a result of it. The reason for exclusion lies in the degree of the impropriety, not in the seriousness of the alleged offending.
 There is an irony in the endorsement of this point. The majority joint judgment in Grant approaches the judge’s task of deciding how to maintain the good repute of the administration of justice by setting out a three-branched decision “tree” (!, at ). These “branches”, or “avenues” (at ) or “lines” ([at ) of inquiry are (1) the seriousness of the impropriety, (2) the impact of the impropriety on the defendant’s rights, and (3) society’s interest in the adjudication of the case on the merits. This third branch or avenue or line excludes the seriousness of the offending, because that “has the potential to cut both ways” (), so as to be an unhelpful consideration. Charter rights operate independently of the type of crime for which the defendant stands accused. So Tipping J in the above passage was quoting what was really a criticism of inclusion of the seriousness of the alleged offending, in the course of explaining how it should be included with the potential of affecting both sides of the balance. Like Deschamps J dissenting () we approach the decision by way of two-arm test in which factors favouring admission are balanced against those favouring exclusion, and it would be preferable for us to treat the seriousness of the offending as a factor favouring admission without seriousness ever favouring exclusion (see Deschamps J at ). I have commented on Grant here on July 18, 2009.
Update: For a diagrammatic representation of the decision process under s 30, see this note (8 January 2021).