III.  RES JUDICATA/COLLATERAL ESTOPPEL

            As generally understood, “[t]he doctrine of res judicata gives certain conclusive effect to a former judgment in subsequent litigation involving the same controversy.”  (7 Witkin, Cal. Procedure (4th ed. 1997) Judgment, § 280, p. 820.)   The doctrine “has a double aspect.”  (Todhunter v. Smith (1934) 219 Cal. 690, 695.)  “In its primary aspect,” commonly known as claim preclusion, it “operates as a bar to the maintenance of a second suit between the same parties on the same cause of action.  [Citation.]”  (Clark v. Lesher (1956) 46 Cal.2d 874, 880.)  “In its secondary aspect,” commonly known as collateral estoppel, “[t]he prior judgment . . . ‘operates’ ” in “a second suit . . . based on a different cause of action . . . ‘as an estoppel or conclusive adjudication as to such issues in the second action as were actually litigated and determined in the first action.’  [Citation.]”  (Ibid.)  “The prerequisite elements for applying the doctrine to either an entire cause of action or one or more issues are the same:  (1) A claim or issue raised in the present action is identical to a claim or issue litigated in a prior proceeding; (2) the prior proceeding resulted in a final judgment on the merits; and (3) the party against whom the doctrine is being asserted was a party or in privity with a party to the prior proceeding.  [Citations.]”  (Brinton v. Bankers Pension Services, Inc. (1999) 76 Cal.App.4th 550, 556.)  Defendant asserts that both aspects of the doctrine bar retrial of his alleged prior conviction. 

          Defendant’s claim raises a threshold issue that we have not yet decided: whether either aspect of the res judicata doctrine “even applies to further proceedings in the same litigation.  [Citation.]”  (People v. Memro (1995) 11 Cal.4th 786, 821.)  As the court observed in Mitchell, “[t]he traditional application of such doctrines [is] to ‘successive prosecutions’ [citation] or rulings from a former action [citation].”  (Mitchell, supra, 81 Cal.App.4th at pp. 147-148.)  For example, as we have explained, appellate court judgments establish the law that “ ‘must be applied in the subsequent stages of the cause’ ”—i.e., the law of the case—“ ‘and they are res adjudicata in other cases as to every matter adjudicated.’ ”  (Dept. of Water & Power v. Inyo Chem. Co. (1940) 16 Cal.2d 744, 750, italics added.)  Relying principally on U.S. v. Bailin (7th Cir. 1992) 977 F.2d 270 (Bailin), defendant asserts that “[f]ederal courts and courts from other states have routinely applied collateral estoppel, or direct estoppel, to bar further proceedings in the same action.”  However, as defendant correctly notes, we specifically questioned Bailin’s holding in People v. Santamaria (1994) 8 Cal.4th 903, 915, footnote 5.  There, after reviewing relevant high court authority, “we question[ed] whether collateral estoppel applies to [retrial in] the same proceeding where the government won by securing a conviction of the substantive count” and the conviction was reversed on appeal.  (Id. at p. 913; see also Memro, supra, 11 Cal.4th at p. 821 [“[i]t is questionable whether the doctrine of collateral estoppel even applies to further proceedings in the same litigation”].)  Ultimately, we did not decide the question in Santamaria because we found that the collateral estoppel claim in that case failed “on the merits” for other reasons.  (Santamaria, supra, 8 Cal.4th at p. 916.)

            Similarly, in this case, we need not resolve this threshold question because defendant’s res judicata claim fails for other reasons.  Initially, we agree with the People that neither aspect of res judicata applies because an appellate reversal, for insufficient evidence, of a true finding regarding an alleged prior conviction or juvenile adjudication does not generally constitute a final decision on the merits regarding the truth of the alleged prior conviction or juvenile adjudication.[5]  As previously discussed, where an appellate court finds that the evidence at trial was insufficient to support the verdict, the “normal rule” is that the losing party on appeal is “entitled to a retrial” unless the record shows “ ‘that on no theory grounded in reason and justice could the party defeated on appeal make a further substantial showing in the trial court in support of his cause.’  [Citations.]”  (Boyle, supra, 71 Cal.2d at pp. 232-233, fn. 3.)  Here, nothing in the record suggests that, at a retrial, the People would be unable to make the necessary showing regarding the declaration of wardship, and defendant has never contended otherwise.[6]  Monge I and Monge II established that such retrials are not precluded by double jeopardy principles, and we found earlier in this opinion that such retrials are not precluded by due process principles or the law of the case doctrine.  Thus, “the Court of Appeal should not have departed from the normal rule that [the People were] entitled to a retrial” on defendant’s alleged prior juvenile adjudication.  (Boyle, supra, 71 Cal.2d at p. 233, fn. 3.)  Given that the Court of Appeal should have ordered a new trial of the alleged prior juvenile adjudication, its reversal of the true finding for insufficient evidence lacks the requisite finality for purposes of applying res judicata or collateral estoppel.  (See Pillsbury v. Superior Court (1937) 8 Cal.2d 469, 472 [appellate order reversing for further proceedings “is not an adjudication in the same sense as a final judgment” for purposes of applying res judicata]; Board of Education v. Fowler (1861) 19 Cal. 11, 26 [appellate decision reversing judgment and remanding is not a “final judgment” that would bar subsequent action].)

            Our conclusion is fully consistent with the high court’s decision in Monge II.  As previously explained, there the high court held that where an appellate court finds insufficient evidence to support a true finding regarding an alleged prior conviction, the order reversing the finding lacks the “ ‘constitutional finality’ ” to trigger double jeopardy protections and, therefore, does not preclude retrial.  (Monge II, supra, 524 U.S. at p. 729.)  The purposes of the double jeopardy and res judicata doctrines substantially overlap.  We have explained that the purposes of the res judicata doctrine include “prevent[ing] inconsistent judgments which undermine the integrity of the judicial system” and “preventing a person from being harassed by vexatious litigation.  [Citation.]”  (People v. Taylor (1974) 12 Cal.3d 686, 695.)  Similarly, the high court has explained that the purposes of the double jeopardy clause include preserving “the integrity of a final judgment” (United States v. Scott (1978) 437 U.S. 82, 92) and protecting individuals “from the harassment and vexation of unbounded litigation.”  (Arizona v. Manypenny (1981) 451 U.S. 232, 246.)  The high court has also observed that “[a] primary purpose served” by the double jeopardy clause—preserving the finality of judgments—“is akin to that served by the doctrines of res judicata and collateral estoppel.”  (Crist v. Bretz (1978) 437 U.S. 28, 33.)  Defendant offers no reason for ignoring these overlapping purposes and refusing to apply, in the res judicata context, Monge II’s holding that an appellate reversal, for insufficient evidence, of a true finding on a prior conviction allegation lacks the requisite finality for purposes of the double jeopardy clause. 

            The conclusion that res judicata does not apply here is also consistent with our prior decision in Mattson.  As previously explained, Mattson held that after an appellate court reverses a conviction because the evidence at trial was insufficient to establish the admissibility of confessions, the prosecution on remand may “relitigate” that issue and “introduce[] evidence [that] had not been presented at the first trial . . . .”  (Mattson, supra, 50 Cal.3d at p. 849.)  In rejecting the defendant’s many arguments against this conclusion, we held that “[n]either constitutional nor ‘equitable’ double jeopardy nor collateral estoppel considerations bar relitigation of the admissibility of defendant’s confessions in this case.”  (Id. at p. 853, fn. 16, italics added.)  Although we did not explain the basis for this conclusion, our holding in Mattson is, nevertheless, inconsistent with defendant’s assertion of collateral estoppel in this case.  In short, because defendant cannot establish one of the threshold requirements for application of res judicata—finality of the prior decision—his attempt to invoke either aspect of that doctrine necessarily fails.[7]