State v. Bryan James Krueger, 2008 WI App 162
For Krueger: Bradley J. Lochowicz
¶15 Here, Mason was asked whether she had formed an opinion as to whether or not S.B. “was the product of any suggestibility or any coaching.” … Signs of coaching or suggestion could fall into the realm of knowledge that is outside that of a lay-person jury. 
¶16 However, in assessing that because S.B. was not highly sophisticated she would not have been able to maintain consistency throughout her interview “unless it was something that she experienced,” Mason testified that S.B. had to have experienced the alleged contact with Krueger. The testimony was tantamount to an opinion that the complainant had been assaulted—that she was telling the truth. As in Haseltine, this testimony simply went too far, and its effect was to usurp the role of the jury in determining credibility. See Haseltine, 120 Wis. 2d at 96; Romero, 147 Wis. 2d at 278; Tutlewski, 231 Wis. 2d at 390. 
¶17 We therefore agree with Krueger that counsel’s performance was deficient in failing to object to Mason’s testimony and that Krueger was prejudiced by counsel’s deficient performance. The appropriate measure of attorney performance is reasonableness, considering all the circumstances. See State v. Brooks, 124 Wis. 2d 349, 352, 369 N.W.2d 183 (Ct. App. 1985). While trial counsel testified that she had not objected because she viewed Mason’s testimony as admissible expert opinion, her view of the law was incorrect. It is well established that an expert witness cannot testify as to the credibility of another witness, and counsel’s failure to object when Mason did so was unreasonable.  Haseltine, 120 Wis. 2d at 96; Strickland, 466 U.S. at 687.
As Judge Brown points out in concurrence, ¶21, the holding is actually quite narrow:
I write separately to underscore that prosecutors will not be hamstrung by this opinion one iota. The opinion simply means that, while expert evidence regarding coaching or the lack of it is allowable, prosecutors must be careful in how they present it. The key word here is “objective.” The questions must be objectively tailored and designed to elicit objective answers. A good starting point for prosecutors would be footnote ten of the majority’s opinion. Certainly, prosecutors can tailor an objective, nonleading question about the child’s “ability to supply peripheral details of the alleged incident.” They can ask about the child’s use of language in describing the assault. They can ask about information “not appropriate for the developmental level of the child.” There are probably many more objective questions a prosecutor can ask that will get the prosecutor’s point across. What the prosecutor cannot do is cross the line by inviting the expert to give her or his opinion about whether the child was coached. In sum, be careful.
One small matter. The court takes pains to note that “Wisconsin law has not yet addressed the precise question of the admissibility of expert opinion testimony about whether the child’s testimony and behavior exhibit signs of coaching or suggestion,” ¶14. That being so, why didn’t the court simply say, “Deficient performance is limited to situations where the law or duty is clear such that reasonable counsel should know enough to raise the issue,” State v. Jennifer Wery, 2007 WI App 169, ¶17, and wash its hands of the matter? Apparently because, in the final analysis, the issue wasn’t all that novel as the court itself ultimately acknowledged: “It is well established that an expert witness cannot testify as to the credibility of another witness, and counsel’s failure to object when Mason did so was unreasonable,” ¶17.