What place do rules have in modern evidence law?
Should the admissibility of evidence of prior misconduct, for which the accused has been tried and acquitted, be determined by a rule, such as issue estoppel, or by a discretion?
That was the main issue in R v Mahalingan  SCC 63 (14 November 2008).
Before looking at how this was addressed in that case, it is worth recalling that the rules of evidence should promote the ascertainment of the truth, that a trial must be fair to the accused but fairness to the prosecution is also important although not overriding, and that evidence of an alleged fact does not have to establish that fact beyond reasonable doubt before it is admissible as part of the case for either side.
This last point is illustrated by Bayes' Theorem.
In Mahalingan the Supreme Court unanimously ordered a retrial on aggravated assault. After the original trial on that charge the accused had been acquitted of attempting to pervert the course of justice, it having been alleged that he had telephoned a witness before the aggravated assault trial and tried to persuade that person not to incriminate him. Should evidence of that alleged telephone conversation be admissible at the retrial on the aggravated assault?
The minority (Deschamps, Abella and Charron JJ) approached this consistently with the propositions about the law of evidence that I have set out above. To be admissible, the evidence of the telephone call need only be established on the balance of probabilities (166).
That standard is applied as a matter of policy, and is not a requirement of logic, as Bayes' Theorem demonstrates.
The minority rejected an argument that the rule concerning issue estoppel should apply in criminal law. Various reasons for this rejection were advanced by Charron J, who delivered the joint judgment of the dissenters. Most importantly she held that (132):
"The application of issue estoppel as an absolute rule precluding the admission of prior acquittal evidence in all cases regardless of context is inconsistent with the basic rule favouring the admission of all relevant evidence, subject to countervailing concerns."
The countervailing concerns are adequately expressed in existing concepts and provisions: abuse of process, character evidence admissibility, rules against multiple convictions and collateral attack, and the pleas of autrefois acquit and autrefois convict; s 11(h) of the Charter is also relevant (84). Such of those matters as were relevant would be considered by the judge at the retrial, and the evidence was not rendered inadmissible by issue estoppel which is only an appropriate rule for civil cases.
McLachlin CJ delivered the judgment of herself and Binnie, LeBel, Fish and Rothstein JJ. Issue estoppel is retained in criminal law but in a revised form (to correct its drift into difficulty) so that it now precludes the prosecution from relitigating an issue that has been resolved in the accused's favour in a previous criminal proceeding, whether on the basis of a positive fact finding or on a reasonable doubt (2, 22, 26).
The policies behind this are the desirability of avoiding inconsistent verdicts, the need to uphold the principle of finality, and the need to ensure fairness to the accused.
This last matter, fairness to the accused, does not mean fairness in the sense of a fair trial, but rather it means fairness in the public policy sense. The Chief Justice elaborated her use of the expression "fairness to the accused" at 39:
"In my view, it is clear that fairness to the accused requires that an accused should not be called upon to answer allegations of law or fact already resolved in his or her favour by a judicial determination on the merits. This is the most compelling rationale for retaining issue estoppel in criminal law, as it goes to the core tenets of our criminal justice system. The state has the right to charge an accused and to prove the facts at a trial of the charge. If a judge or jury conclusively decides a fact in favour of the accused, including via a finding of a reasonable doubt on an issue, then the accused should not be required in a subsequent proceeding to answer the same allegation. To require, in effect, a second defence of the issue would be to violate the fundamental function of res judicata."
This requires a determination, in each case, of whether the issue in question has been previously decided in the accused's favour (33):
"Only issues that were either necessarily resolved in favour of the accused as part of the acquittal, or on which findings were made (even if on the basis of reasonable doubt) are estopped."
That, I suggest, will operate capriciously. The accused has the burden of showing that the issue was decided in his favour (23), and his ability to meet this burden may depend on what he was previously charged with, and how many issues he raised at the earlier trial. He might diminish his chances of successfully relying on issue estoppel if he raised multiple issues, even though a genuinely innocent accused would put everything in issue.
In New Zealand we have crept away from issue estoppel in criminal law: R v Davis  1 NZLR 584 (CA), Bryant v Collector of Customs  1 NZLR 280 (CA), R v Coombs  1 NZLR 318 (CA), R v Fatu  3 NZLR 419 (CA), R v Degnan  1 NZLR 280 (CA), Fox v A-G  3 NZLR 62 (CA). See also Z v Dental Complaints Assessment Committee  NZSC 55 (blogged here 25 July 2008) especially at paras 57-59, 125-127, for discussion of the use of criminally determined matters in civil proceedings, a topic also addressed in abuse of process terms, without reference to issue estoppel. That trend suggests that the minority approach in Mahalingan would be favoured here. We have regarded the jurisdiction to prevent an abuse of process by, inter alia, excluding evidence on public policy grounds, as a potentially powerful means of ensuring fairness in the wider sense. This contrasts with the majority judgment in Mahalingan, where abuse of process was described as a broad, somewhat vague concept that varies with the eye of the beholder, reserved for obviously egregious abuses of the Crown power, to be relied on successfully only extremely rarely (42):
"To protect parties from relitigation, abuse of process would need to be cast in a less discretionary form than it now takes. Therefore, considering the high threshold for proof and the unpredictability of its operation, it is unlikely that the doctrine of abuse of process adequately achieves the fairness goal that underlies the doctrine of issue estoppel."
That may reflect the emaciated form of the abuse of process jurisdiction in Canada. In other legal systems it may be relatively (I feel I am entitled to use the word "relatively" in view of my recent brush with smugness) strong and an adequate substitute for the rule against issue estoppel.
I should add, lest I be accused of regarding Canadian law as unduly flaccid, that the Charter provides the remedy of discretionary exclusion (s 24(2)) in terms that will usually make resort to the common law unnecessary: R v O’Connor (1995) 103 CCC(3d) 1 (SCC) per L’Heureux-Dube J at para 70-72. Under s 24(2) the determination is whether admission of evidence obtained in a manner that infringed or denied a Charter right or freedom would bring the administration of justice into disrepute. Common themes had been evident between the common law and Charter jurisprudence. For example, in R v Mack (1990) 44 CCC(3d) 513 (SCC) Lamer J, for the Court, addressed police conduct of an investigation that amounted to entrapment, and held that admitting evidence obtained through such conduct would bring the administration of justice into disrepute. He noted (para 77) that the same principle applied with respect to the common law doctrine of abuse of process. The dominance of the Charter does not render irrelevant Lamer J’s statement of basic principles in Mack.
Nevertheless, the majority in Mahalingan seem to distrust the usefulness of abuse of process. True it is that criticisms for vagueness can always be levelled at concepts that can only be expressed in general terms. Harmless fun can be had in making such criticisms, as occurred in argument in Ngan v R SC8/2007, 14 August 2007 at pp 32-33 (jibes which misfire, as the “high sounding principles” in the Charter are also in the New Zealand Bill of Rights Act 1990). And Blanchard J, the jester in that argument, set out his own general principles in R v Shaheed  2 NZLR 377 (CA) in defining the criterion for discretionary exclusion of improperly obtained evidence, a formulation that has been adopted in s 30(2)(b) Evidence Act 2006[NZ]: “...determine whether or not the exclusion of the evidence is proportionate to the impropriety by means of a balancing process that gives appropriate weight to the impropriety but also takes proper account of the need for an effective and credible system of justice.” [emphasis added; cf para 156 of Shaheed]
Judges do have a sense of what such general concepts mean. As cases applying them accumulate, patterns emerge and these aid the prediction of how the general concepts will work in particular instances.