"The beyond-a-reasonable-doubt standard of Chapman 'requires the beneficiary of a federal constitutional error to prove beyond a reasonable doubt that the error complained of did not contribute to the verdict obtained.' (Chapman v. California (1967) 386 U.S. 18.) 'To say that an error did not contribute to the ensuing verdict is . . . to find that error unimportant in relation to everything else the jury considered on the issue in question, as revealed in the record.' (Yates v. Evatt (1991) 500 U.S. 391, 403.) Thus, the focus is what the jury actually decided and whether the error might have tainted its decision. That is to say, the issue is 'whether the . . . verdict actually rendered in this trial was surely unattributable to the error.' (Sullivan v. Louisiana (1993) 508 U.S. 275, 279.) "In Chapman, the court stated that 'error in admitting plainly relevant evidence which possibly influenced the jury adversely to a litigant cannot . . . be conceived of as harmless.' (Chapman, supra, 386 U.S. at p. 24.) Even if, as a general matter, Chapman's statement might appear overly broad, in the specific context of a confession it carries its greatest force. Indeed, in People v. Cahill (1993) 5 Cal.4th 478, we expressed a 'recognition that confessions, "'as a class,'" "'almost invariably'" will provide persuasive evidence of a defendant's guilt , . . . that such confessions often operate "'as a kind of evidentiary bombshell which shatters the defense'" , . . . and therefore that the improper admission of a confession is much more likely to affect the outcome of a trial than are other categories of evidence, and thus is much more likely to be prejudicial. . . .' (Id. at p. 503.) We acknowledged, however, that the erroneous admission of any given confession 'might be found harmless, for example, (1) when the defendant was apprehended by the police in the course of committing the crime, (2) when there are numerous, disinterested reliable eyewitnesses to the crime whose testimony is confirmed by a wealth of uncontroverted physical evidence, or (3) in a case in which the prosecution introduced, in addition to the confession, a videotape of the commission of the crime. . . .' (Id. at p. 505.) But we emphasized that although the erroneous admission of a confession might be harmless in a particular case, it nevertheless is 'likely to be prejudicial in many cases.' (Id. at p. 503.)" (People v. Neal, supra, 31 Cal.4th at pp. 86-87.)