Collateral estoppel ordinarily bars the relitigation of an issue decided at a previous proceeding when the following threshold requirements are satisfied: "1) the issue to be precluded must be identical to that decided in the prior proceeding; 2) the issue must have been actually litigated at that time; 3) the issue must have been necessarily decided; 4) the decision in the prior proceeding must be final and on the merits; and 5) the party against whom preclusion is sought must be in privity with the party to the former proceeding." (People v. Garcia (2006) 39 Cal.4th 1070.) Nonetheless, because collateral estoppel is ultimately subject to considerations of public policy, the doctrine's application is not automatic. (Lucido, supra, 51 Cal.3d at pp. 342-343.) As our Supreme Court explained in Lucido v. Superior Court (1990) 51 Cal.3d 335, "the public policies underlying collateral estoppel--preservation of the integrity of the judicial system, promotion of judicial economy, and protection of litigants from harassment by vexatious litigation--strongly influence whether its application in a particular circumstance would be fair to the parties and constitutes sound judicial policy." (Id. at p. 343.) Lucido v. Superior Court (1990) 51 Cal.3d 335 is the leading case on the collateral estoppel effects of decisions in probation revocation proceedings, which differ from criminal prosecutions (People v. Clark (1996) 51 Cal.App.4th 575, 581-582, disapproved on another ground in People v. Mendez (1999) 19 Cal.4th 1084, 1098). In Lucido, the defendant was charged with indecent exposure. (Lucido, supra, 51 Cal.3d at p. 339.) At a probation revocation hearing prior to the trial of the offense, the court found that the prosecution had failed to prove a probation violation based on the offense. (Ibid.) After the court declined to dismiss the charges on the ground of collateral estoppel, the defendant sought relief by writ petition. (Id. at p. 341.) The Supreme Court held that the decision at the revocation hearing did not bar the trial, reasoning that although the threshold requirements for collateral estoppel were "arguably" satisfied, public policy precluded the doctrine's application. (Id. at pp. 341-343, 347-351.) In assessing the first category of public policy, namely, the integrity of the judicial system, the court concluded that permitting a revocation hearing to displace a criminal trial as the principal forum for determining criminal culpability would erode public confidence in the judicial system. (Lucido, supra, 51 Cal.3d at p. 347.) The court noted that confidence in the judicial system may be undermined when two tribunals render different verdicts, but reasoned that differences in the determinations at a revocation hearing and a trial would not have this effect, as the two proceedings serve different interests and purposes. (Id. at pp. 347, 350.) The court observed that "a criminal prosecution seeks conviction for wholly new offenses," whereas "a revocation hearing arises as a continuing consequence of the probationer's original conviction ... ." (Id. at p. 348.) As a result, the trial court's fundamental role at a revocation hearing "is not to determine whether the probationer is guilty or innocent of a crime, but whether a violation of the terms of probation has occurred and, if so, whether it would be appropriate to allow the probationer to continue to retain his conditional liberty." (Ibid.) In addition, because "the limited nature of this inquiry" may inhibit the prosecution from presenting a full evidentiary showing at a revocation hearing, the prosecution's failure to satisfy the lower burden of proof at the hearing "does not necessarily amount to an acquittal." (Ibid.) The Supreme Court concluded: "Given these distinctions between the revocation hearing and a criminal trial, application of collateral estoppel would not serve the public interest in holding probationers accountable for both violation of the terms of their probation and commission of newly alleged crimes. Preemption of trial of a new charge by a revocation decision designed to perform a wholly independent social and legal task would undermine the function of the criminal trial process as the intended forum for ultimate determinations as to guilt or innocence of newly alleged crimes. " (Lucido, supra, 51 Cal.3d at pp. 348-349.) Turning to the remaining categories of public policy, the court concluded that concerns about judicial economy and vexatious litigation did not favor the application of collateral estoppel to revocation decisions. The court determined that the importance of preserving the criminal trial process as the "exclusive forum" for litigating new criminal offenses outweighed the efficiencies gained by applying the doctrine. (Lucido, supra, 51 Cal.3d at pp. 350-351.) Furthermore, the court concluded that rejecting the doctrine's application would not promote vexatious or unfair litigation: "The essence of vexatiousness ... is not mere repetition. Rather, it is harassment through baseless or unjustified litigation. Petitioner does not assert that the criminal proceedings in this case are intended to harass. The public has a legitimate expectation that a person once found guilty of a crime may both be held to the terms of his probation and ... tried anew for any offenses alleged to have been committed during the probationary period." (Id. at p. 351.) In addition, the court noted that a probationer's testimony at a revocation hearing is inadmissible at a subsequent trial. (Ibid.) The court thus held that the decision at the probationer's revocation hearing did not collaterally estop his second trial. (Ibid.) In People v. Garcia (2006) 39 Cal.4th 1070, the California Supreme Court reaffirmed that DSS hearings, unlike probation revocation hearings, may properly displace "the criminal trial process as the intended forum for ultimate determinations as to guilt or innocence of newly alleged crimes" (Lucido, supra, 51 Cal.3d at p. 349). There, a welfare recipient was exonerated of welfare fraud charges at a DSS hearing, but failed to obtain a dismissal of a related criminal action against her, and was convicted of fraud. (Garcia, supra, 39 Cal.4th at pp. 1075-1076.) Relying on People v. Sims (1982) 32 Cal.3d 468, the Supreme Court held that the conviction must be reversed. (Id. at pp. 1076-1083.) In reaching this conclusion, the Supreme Court rejected the contention that Sims should be overruled because amendments to the DSS statutory scheme had erased the legislative preference that welfare fraud allegations be resolved in DSS proceedings. (Garcia, supra, 39 Cal.4th at pp. 1076-1083.) Notwithstanding the amendments, the court identified other factors justifying the distinction between DSS proceedings and revocation hearings, for purposes of collateral estoppel. (Id. at pp. 1085-1087.) Noting the discussion in Lucido regarding the integrity of the judicial system, the court explained that DSS proceedings and revocation hearings serve different interests and purposes: DSS proceedings, like criminal trials, provide forums for the determination of culpability regarding new offenses, but revocation hearings do not. (Id. at pp. 1086-1087.) On this matter, the court remarked: "In essence, the issue at a probation revocation hearing is whether the defendant's conduct demonstrates that the leniency extended by the grant of probation remains justified. By contrast, ... 'a criminal prosecution seeks conviction for wholly new offenses.' " (Id. at p. 1087, quoting Lucido, supra, 51 Cal.3d at p. 348.) The Garcia court also distinguished DSS proceedings from revocation hearings on two points related to the policy concern regarding vexatious litigation. (Garcia, supra, 39 Cal.4th at pp. 1085-1086.) First, forcing welfare recipients to respond to criminal charges after successfully defending fraud allegations in DSS proceedings would impose a hardship on them; in contrast, no such hardship attaches to a criminal trial following a revocation hearing. (Id. at pp. 1085-1086.) Second, a probationer's testimony at a revocation hearing is inadmissible at a subsequent trial, whereas welfare recipients enjoy no such protection regarding their testimony at DSS proceedings. (Id. at p. 1086.)