Witness Credibility: Impeachment of Police Officer Witnesses with Prior Misconduct and/or Dishonesty
July 19th, 2018

Among the factors affecting a witnesses’ credibility listed in CC 105 are the following:


–[Did the witness admit to being untruthful?]

–[What is the witness’s character for truthfulness?]

–[Has the witness been convicted of a felony?]

–[Has the witness engaged in [other] conduct that reflects on his or her believability?]


Similarly, CC 316 tells the jurors that if “a witness has committed a crime or other misconduct, you may consider that fact [only] in evaluating the credibility of the witness’s testimony.”


Hence when a police witness testifies for the prosecution the defense has the right to fully investigate his or her prior misconduct. For example, Milke v. Ryan (9th Cir. March 14, 2013) 711 F.3d 998: overturned a murder conviction because the prosecution failed to disclose the lead detective’s “long history of lying under oath and other misconduct.” “Multiple judicial determinations that [the detective] had lied in performing his official functions and violated suspects’ constitutional rights would have been highly relevant where the state’s case rested on his testimony.”  (Id. at 1008.) Brady and Giglio required disclosure of all of this information to defendant.  (711 F.3d at p. 1003; cf., (Brown v. Muniz (9th Cir. 2018) 889 F.3d 661, 675-676 [conviction upheld where police witnesses participation in the case was “tangential at best”].)

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