Chapter 4 - §3. Specific types of impeachment evidence

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§3. Specific types of impeachment evidence

§3.1. Demeanor. A witness's credibility can be attacked or supported by her demeanor (e.g., facial expressions, gestures, tone, attire) while testifying and the manner in which she testifies. Evid. C. §780(a); People v. Caro (2019) 7 Cal.5th 463, 511; People v. Lopez (2013) 56 Cal.4th 1028, 1064, overruled on other grounds, People v. Rangel (2016) 62 Cal.4th 1192; see People v. Garton (2018) 4 Cal.5th 485, 501 (although jewelry is not typically part of witness's demeanor, wedding ring conveys specific meaning, and its presence or absence may be relevant to credibility in some cases); People v. Scott (2011) 52 Cal.4th 452, 493 (demeanor is always relevant to witness's credibility). Although the jury's observation of a witness's demeanor while testifying is not technically evidence, the jury is expressly authorized to consider the witness's demeanor in evaluating her credibility, and attorneys can comment on those matters in argument. See Evid. C. §780(a); see, e.g., People v. Jackson (1989) 49 Cal.3d 1170, 1205-06 (no error when prosecutor commented on D's smirking manner while on witness stand). However, the jury can consider a witness's demeanor only to the extent of what they observe and hear inside the courtroom. See People v. Anderson (2018) 5 Cal.5th 372, 408-09. As with a witness's testimony, a witness's demeanor can also be impeached. People v. Jones (1998) 17 Cal.4th 279, 306-07. Any evidence offered to rebut an implied statement derived from a witness's demeanor (such as the implied statement of remorse derived from crying on the witness stand) must relate directly to a particular incident or character trait that the defendant has previously offered on his own behalf. Id. at 307.


Although commenting on a testifying witness's behavior is proper for evaluating her credibility, commenting on a nontestifying defendant's demeanor during the trial's guilt phase, other than to simply say that the jury should ignore it, is improper. People v. Boyette (2002) 29 Cal.4th 381, 434.

§3.2. Character of testimony. A witness's credibility can be attacked or supported by the character of her testimony. Evid. C. §780(b). For example, a witness can be impeached by a showing that her testimony is inconsistent with common sense, experience, or established facts. See, e.g., People v. Mora (2018) 5 Cal.5th 442, 479 (defense witness's testimony that recording of her interview with police was stopped and started was impeached by playing unredacted interview recording); People v. Panah (2005) 35 Cal.4th 395, 479 (defense witness's testimony that she was coerced by detective into talking about D was impeached by evidence that she had asked detective for help in obtaining her release). Whether a witness can be asked during cross-examination if another witness was lying depends on the circumstances and context of the examination. See People v. Chatman (2006) 38 Cal.4th 344, 384. A court may permit such questions if the witness has personal knowledge that allows her to provide competent testimony that may legitimately assist the trier of fact in resolving credibility questions. Id. But a court should exercise discretion and prevent such "Were they lying?" questions when they are argumentative or designed to elicit a speculative response. Id.

§3.3. Capacity to perceive, recollect, or communicate. A witness's credibility can be attacked or supported by her ability to perceive, recollect, or communicate any matter about which she testifies. Evid. C. §780(c); see People v. Nieves (2021) 11 Cal.5th 404, 474 (question to chaplain about how infrequently she testified for the thousands of inmates to whom she ministered was relevant to credibility); People v. Rodriguez (1999) 20 Cal.4th 1, 9 (witness's capacity to observe is always relevant to impeachment). For example, a witness's capacity to perceive can be impeached by evidence that she was unable to clearly see an event due to impaired eyesight or was unable to clearly hear dialogue because of poor hearing. Similarly, a witness's capacity to accurately recollect can be impeached by evidence that she cannot remember important details of the event in question or that her memory is generally inaccurate or incomplete.


A person's competence to testify as a witness and her credibility involve similar, but distinct, issues. Whether a person is competent to testify is a preliminary issue determined solely by the court. See Evid. C. §700; People v. Montoya (4th Dist.2007) 149 Cal.App.4th 1139, 1150; People v. Knox (1st Dist.1979) 95 Cal.App.3d 420, 431. See "Competency," ch. 2, §1.1.1. If the court finds the witness competent to testify, then the determination of whether the witness had the ability to accurately perceive or recollect and whether she communicated truthfully and accurately are issues of credibility to be determined exclusively by the trier of fact. Knox, 95 Cal.App.3d at 431.

1. Mental illness or disease. Evidence that a witness was or is insane or that her memory or mind is impaired by another disease is admissible to impeach her capacity to perceive and recollect. See, e.g., People v. Lewis (2001) 26 Cal.4th 334, 356-57 (D impeached eyewitness by demonstrating that witness's mental infirmities affected his abilities to perceive, recollect, and communicate); People v. La Rue (3d Dist.1923) 62 Cal.App. 276, 284 (court erred when it prevented D from cross-examining witness about his recent treatment for disease that causes insanity). But a court cannot compel any witness (or any victim of sexual assault) to submit to a psychiatric or psychological examination for the purpose of assessing her credibility. Pen. C. §1112.

2. Drug or alcohol use. Evidence that a witness was under the influence of drugs or alcohol when she observed the event in question, or while she is testifying, is admissible to impeach her capacity to perceive, recollect, or communicate from the witness stand. See People v. Anderson (2018) 5 Cal.5th 372, 399-400; People v. Melton (1988) 44 Cal.3d 713, 737; People v. Crow (2d Dist.1941) 48 Cal.App.2d 666, 671; see, e.g., In re Hardy (2007) 41 Cal.4th 977, 1025 (prosecution's witness was impeached by evidence that she had passed out due to drugs and alcohol on night of murder). Evidence that a witness is a habitual user of drugs or alcohol, however, is generally not admissible to impeach the witness's ability to perceive or recollect unless there is expert testimony on the probable effect of such use on her faculties. People v. Balderas (1985) 41 Cal.3d 144, 191; see, e.g., People v. Wilson (2008) 44 Cal.4th 758, 794 (evidence that witness was habitual methamphetamine user was properly excluded when there was no evidence that witness ingested drug on day of crimes and no expert testimony was presented to explain its long-term effect on one's ability to perceive or recall); cf. People v. Johnigan (2d Dist.2011) 196 Cal.App.4th 1084, 1095 (expert testimony that if intoxicated person could not recall something from short-term memory, then her recollection of subject matter at later date was unlikely, was struck because expert could not show adequate foundation for opinion).


Unless the defendant can demonstrate probable cause to believe that a witness is under the influence of drugs or alcohol at the time of her testimony, the defendant's constitutional right to confront witnesses does not permit the court to order the witness to submit to a blood or urine test. See Anderson, 5 Cal.5th at 399-400; Melton, 44 Cal.3d at 737-38. Without probable cause, the defendant's confrontation right does not outweigh the witness's right to remain free of unreasonable searches or seizures of her bodily fluids. See Melton, 44 Cal.3d at 738-39 & n.7 (explaining that such intrusions also require that "the likelihood and importance of recovering the evidence" outweigh "the degree of intrusion" of the witness's body, but declining to decide whether showing of necessity for urine testing might be less stringent than that required for blood testing).

§3.4. Opportunity to perceive. A witness's credibility about her personal knowledge of any matter she testifies to can be attacked or supported by the extent of her opportunity to perceive the matter. Evid. C. §780(d). For example, a party can cross-examine a witness who claims to have seen an incident on whether her observations were impaired by some physical obstruction or by extreme weather.

§3.5. Character trait of dishonesty or truthfulness. A witness's credibility can be supported by evidence of her character for truthfulness or attacked by evidence of a character trait that shows her dishonesty or lack of veracity. Evid. C. §780(e); People v. Hines (4th Dist.2020) 58 Cal.App.5th 583, 609; e.g., People v. Bell (2019) 7 Cal.5th 70, 106-07 (mother of witness properly permitted to provide character evidence of witness's reputation for honesty among family members). Generally, this can be accomplished by using opinion evidence, reputation evidence, or evidence of specific instances of the witness's conduct. See Evid. C. §1100. See "Permitted types—Generally," ch. 4-A, §1.3.1(1). Before 1982, a felony conviction was the only category of specific misconduct that could be used to impeach a witness. See Evid. C. §§787, 788. But that restriction was removed for criminal proceedings after the passage of Proposition 8 (Victims' Bill of Rights) in 1982. See "After Proposition 8," ch. 4-B, §2.2.1(2)(b). Now, a witness's credibility can be impeached by (1) felony convictions and (2) other acts of misconduct.

Federal Comparison

The FREs also allow a witness to be impeached by her character for untruthfulness. See FRE 608(a). Extrinsic evidence offered to show a witness's character for untruthfulness, however, can only be in the form of opinion or reputation testimony; it cannot be in the form of testimony about specific instances of misconduct unless it concerns a criminal conviction. FRE

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