Holding that the district court erred in admitting testimony of an expert who "stated that he ‘rejected’ the possibility that [law-enforcement witnesses] had lied, and explained various reasons why police officers have no incentive to give false statements in excessive force cases"
Holding that a record consisting of a preliminary report, an amended report, an affidavit prepared to meet the adversary's Daubert challenge, and multiple depositions was sufficient to obviate the need for a Daubert hearing
Holding that after a defendant identifies a plausible alternative cause, it is "necessary for the plaintiffs expert to offer a good explanation as to why his or her conclusion remains reliable"