The following excerpt is from Figueroa v. Mazza, 825 F.3d 89 (2nd Cir. 2016):
A police officer is under a duty to intercede and prevent fellow officers from subjecting a citizen to excessive force, and may be held liable for his failure to do so if he observes the use of force and has sufficient time to act to prevent it. O'Neill v. Krzeminski, 839 F.2d 9, 1112 (2d Cir. 1988). Liability attaches on the theory that the officer, by failing to intervene, becomes a "tacit collaborator" in the illegality. See id.
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