In People v Arnold (96 NY2d 358, 363) the Court of Appeals held that when a prospective juror makes a statement or statements that "cast serious doubt on [his or her] ability to render an impartial verdict" (People v Arnold, 96 NY2d 358, 363), that prospective juror must be excused for cause unless he or she provides an "unequivocal assurance that [he or she] can set aside any bias and render an impartial verdict based on the evidence" While no "particular expurgatory oath or talismanic' words [are required,] . . . jurors must clearly express that any prior experiences or opinions that reveal the potential for bias will not prevent them from reaching an impartial verdict" (Arnold, 96 NY2d at 362). In People v Lewis (2010 NY Slip Op 02624 [4th Dept 3/26/10])the Fourth Department applied Arnold in the context of the common situation in which prospective jurors state that they would tend to favor the testimony of police witnesses over that of other witnesses:

During voir dire, one of the prospective jurors stated that, as a result of her close association with police officers in the course of her work as a loss prevention officer, she would "probably take the word of a cop" over "the word of somebody else." When defense counsel asked that prospective juror whether she would "tend to give the——the cop the edge on who's telling the truth," she responded, "I would lean that way, yes." There is no question that those statements cast serious doubt on the prospective juror's ability to render an impartial verdict (citations omitted), and the prospective juror failed to provide "unequivocal assurance that [she could] set aside any bias and render an impartial verdict based on the evidence" (citation omitted). The prior collective acknowledgment by the jury panel that the panel members would decide the case solely on what they heard and saw in the courtroom and not based upon any relationships with law enforcement "was insufficient to constitute such an unequivocal declaration" (citations omitted).
With respect to the second prospective juror, the record reflects that she expressed uncertainty about her ability to be fair and impartial as a result of her close relationships with members of law enforcement. When defense counsel attempted to explore the prospective juror's apparent reservations, the court precluded any further inquiry on the matter. Although there is no question that a trial court "necessarily has broad discretion to control and restrict the scope of the voir dire examination" (People v Boulware, 29 NY2d 135, 140, rearg denied 29 NY2d 670, cert denied 405 US 995; see People v Habte, 35 AD3d 1199), we conclude under the circumstances of this case that the court erred in failing to permit defense counsel to conduct further questioning of the prospective juror to determine whether she could provide an "unequivocal assurance" of her ability to render a fair and impartial verdict, or to excuse the prospective juror for cause(citations omitted).

Importantly the reason that the Court was able to reverse was that the defendant had exhausted all of his peremptory challenges before the completion of jury selection.