Section 906.08. Evidence of character and conduct of witness.

 

(1)   Opinion and reputation evidence of character. Except as provided in s. 972.11 (2) , the credibility of a witness may be attacked or supported by evidence in the form of reputation or opinion, but subject to the following limitations:

(a) The evidence may refer only to character for truthfulness or untruthfulness.

(b) Except with respect to an accused who testifies in his or her own behalf, evidence of truthful character is admissible only after the character of the witness for truthfulness has been attacked by opinion or reputation evidence or otherwise.

(2)   Specific instances of conduct. Specific instances of the conduct of a witness, for the purpose of attacking or supporting the witness's credibility, other than a conviction of a crime or an adjudication of delinquency as provided in s. 906.09 , may not be proved by extrinsic evidence. They may, however, subject to s. 972.11 (2) , if probative of truthfulness or untruthfulness and not remote in time, be inquired into on cross-examination of the witness or on cross-examination of a witness who testifies to his or her character for truthfulness or untruthfulness.

(3)   Testimony by accused or other witnesses. The giving of testimony, whether by an accused or by any other witness, does not operate as a waiver of the privilege against self-incrimination when examined with respect to matters which relate only to credibility.

Sup. Ct. Order, 59 Wis. 2d R1, R171 (1973); 1975 c. 184 , 421 ; 1991 a. 32 ; 1995 a. 77 , 225 . The trial court committed plain error by admitting extrinsic impeaching testimony on a collateral issue. McClelland v. State, 84 Wis. 2d 145 , 267 N.W.2d 843 (1978). When credibility of a witness was a critical issue, exclusion of evidence offered under sub. (1) was grounds for discretionary reversal. State v. Cuyler, 110 Wis. 2d 133 , 327 N.W.2d 662 (1983). Impeachment of an accused by extrinsic evidence on a collateral matter was harmless error. State v. Sonnenberg, 117 Wis. 2d 159 , 344 N.W.2d 95 (1984). Absent an attack on credibility, a complainant's testimony that she had not initiated a civil action for damages was inadmissible when used to bolster credibility. State v. Johnson, 149 Wis. 2d 418 , 439 N.W.2d 122 (1989), confirmed, 153 Wis. 2d 121 , 449 N.W.2d 845 (1990). Allegations of professional misconduct against the prosecution's psychiatric expert initially referred to the prosecutor's office but immediately transferred to a special prosecutor for investigation and possible criminal proceedings were properly excluded as a subject of cross-examination of the expert due to a lack of logical connection between the expert and the prosecutor necessary to suggest bias. State v. Lindh, 161 Wis. 2d 324 , 468 N.W.2d 168 (1991). Whether a witness's credibility has been sufficiently attacked to constitute an attack on the witness's character for truthfulness permitting rehabilitating character testimony is a discretionary decision. State v. Anderson, 163 Wis. 2d 342 , 471 N.W.2d 279 (Ct. App. 1991). Evidence that an expert in a medical malpractice action was named as a defendant in a separate malpractice action was inadmissible for impeachment purposes under this section because it did not cast light on the expert's character for truthfulness. Nowatske v. Osterloh, 201 Wis. 2d 497 , 549 N.W.2d 256 (Ct. App. 1996), 93-1555 . Character evidence may be allowed under sub. (1) (b) based on attacks on the witness's character made in opening statements. Allegations of a single instance of falsehood cannot imply a character for untruthfulness. The attack on the witness must be an assertion that the witness is a liar generally. State v. Eugenio, 219 Wis. 2d 391 , 579 N.W.2d 642 (1998), 96-1394 . It was appropriate for an expert to testify to the nature of witnesses' cognitive disabilities and how those mental impairments affected the witnesses' ability to testify or recall particular facts, but the expert's testimony that the witnesses were incapable of lying violated the rule that a witness is not permitted to express an opinion on whether another physically and mentally competent witness is telling the truth. State v. Tutlewski, 231 Wis. 2d 379 , 605 N.W.2d 561 (1999), 98-2551 . Evidence that a witness belongs to an organization, such as a street gang, is admissible to impeach the witness's testimony by showing bias. State v. Long, 2002 WI App 114 , 255 Wis. 2d 729 , 647 N.W.2d 884 , 01-1147 . Asking a defendant whether his or her accusers, a citizen witness, or an investigating police officer are telling the truth has no tendency to usurp the jury's function in assessing credibility; indeed, if anything, it would help the jury evaluate each witness's demeanor. State v. Bolden, 2003 WI App 155 , 265 Wis. 2d 853 , 667 N.W.2d 364 , 02-2974 . The opinion of an expert witness about whether another competent witness is telling the truth serves no useful purpose, and may be detrimental to the process because the jury does not need any expert assistance in assessing credibility. When a prosecutor's cross-examination of a defendant's eyewitness account was to impeach the defendant's credibility by asking whether another eyewitness account was untruthful and not to bolster the credibility of the other witness, because both and the other witness were testifying to their personal observations about the same events, the cross-examination of the defendant was permissible. State v. Johnson, 2004 WI 94 , 273 Wis. 2d 626 ; 681 N.W.2d 901 , 02-2793 .