What is the test for a judge to declare a mistrial in a case of mistaken identity?

The Judge's subjective appraisal of some remote possibility of bias was completely without the ambit of the well-established rule that 'manifest necessity' must be shown in justification of a mistrial in circumstances such as these (United States v. Perez, 9 Wheat. (22 U.S.) 579, 580, 6 L.Ed. 165; Matter of Nolan v. Court of [292 N.E.2d 781] Gen. Sessions, 11 N.Y.2d 114, 118, 227 N.Y.S.2d 1, 3, 181 N.E.2d 751, 752). So radical an action requires a 'scrupulous exercise of judicial discretion', after consideration of the 'vital competing interests' of the prosecution and the accused (United States v. Jorn, 400 U.S. 470, 485, 486, 91 S.Ct. 547, 27 L.Ed.2d 543). 'Yet, in the final analysis, the judge must always temper the decision whether or not to abort the trial by considering the importance to the defendant of being able, once and for all, to conclude his confrontation with society through the verdict of a tribunal he might believe to be favorably disposed to his fate' (Id., p. 486, 91 S.Ct. p. 558).