Expert Witnesses in Michigan Child Sexual Abuse Cases

In a Michigan child sexual abuse trial, an expert witness may help jurors understand evidence, but may not tell them whom to believe. The Michigan Supreme Court's rule from People v Peterson is that an expert may not testify that the abuse occurred, may not vouch for the complainant's truthfulness, and may not testify whether the defendant is guilty.^[1] In 2019 the Court applied the same idea, in People v Thorpe, to testimony that children overwhelmingly do not lie about abuse and, in the companion case People v Harbison, to a medical "diagnosis" of abuse made without physical findings.^[3][4][6]

This page relies on the Michigan Judicial Institute's benchbooks for the wording of the cases and quotes the passages it relies on. It covers behavioral experts, physicians, nurse examiners and police witnesses. It does not cover DNA or other laboratory science; see DNA evidence in sex crime cases.

The starting point: MRE 702

Any expert opinion has to pass the general rule on expert testimony. A witness qualified "by knowledge, skill, experience, training, or education" may give an opinion if the side offering it shows that it is more likely than not that the expert's specialized knowledge will help the trier of fact, the testimony is based on sufficient facts or data, it is the product of reliable principles and methods, and the opinion reflects a reliable application of them to the facts of the case.^[7]

Three things an expert may never say

The Sexual Assault Benchbook quotes Peterson, a 1995 Michigan Supreme Court decision, for the limits in childhood sexual abuse cases:^[1]

1. "an expert may not testify that the sexual abuse occurred,"^[1]
2. "an expert may not vouch for the veracity of a victim,"^[1]
3. "an expert may not testify whether the defendant is guilty."^[1]

The benchbook gives two Court of Appeals examples of testimony that crossed the line. In one, an expert testified that a child's reaction to anatomically correct dolls demonstrated that the child had been abused. In the other, two experts' testimony indicating that the child had been sexually abused went beyond relating whether behavior was consistent with that of other victims and amounted to "opinions on an ultimate issue of fact, which is for the jury's determination alone."^[8]

What a behavioral expert may say

Peterson also describes what is allowed. In childhood sexual abuse cases "the prosecution may present evidence, if relevant and helpful, to generally explain the common postincident behavior of children who are victims of sexual abuse."^[9]

Kind of testimony	When it is allowed
Typical and relevant symptoms of child sexual abuse	In the prosecution's case in chief, "for the sole purpose of explaining a victim's specific behavior that might be incorrectly construed by the jury as inconsistent with that of an actual abuse victim"[2]
That this complainant's behavior is consistent with that of other child sexual abuse victims	Only when the defendant raises the issue of the child's post-incident behavior, or when the defendant attacks the child's credibility[10]

The second kind of testimony is described in Peterson as rebuttal: an expert may testify about consistencies between the particular victim's behavior and that of other victims "to rebut an attack on the victim's credibility."^[11] The benchbook adds that before admitting any expert testimony about a child's behaviors, the court must determine its relevance and probative value under MRE 401 and MRE 403.^[11]

People v Lukity, a 1999 Supreme Court case, is the benchbook's illustration. The defendant questioned the complainant's credibility and attributed her suicide attempt to problems other than the alleged abuse, so expert testimony was properly admitted to explain general characteristics of sexual abuse victims, including the opinion that her behavior was consistent with that of other victims. The expert also acknowledged that some of those characteristics were consistent with other types of trauma.^[12]

Delayed disclosure

One behavior that comes up is a delay in telling anyone. The benchbook quotes the Court of Appeals: "'Delayed disclosure' refers to sex abuse victims, including children, not immediately informing others of the abuse that transpired."^[13] The legal consequences of delay, including the time limits for bringing charges, are covered in delayed reporting of sexual assault.

What the prosecutor may argue

Peterson allows the prosecution, in commenting on the evidence, to "argue the reasonable inferences drawn from the expert's testimony and compare the expert testimony to the facts of the case."^[9]

People v Thorpe: no statistics on truthfulness

In 2019 the Michigan Supreme Court decided People v Thorpe. The Sexual Assault Benchbook quotes the holding: "expert witnesses may not testify that children overwhelmingly do not lie when reporting sexual abuse because such testimony improperly vouches for the complainant's veracity."^[3] The Court reversed the judgment of the Court of Appeals and remanded for a new trial.^[3]

The benchbook also quotes the Court's description of what happened at trial. The expert "identified only two specific scenarios in his experience when children might lie, neither of which applie[d to the] case," so that "one might reasonably conclude on the basis of [the expert's] testimony that there was a 0% chance [the complainant] had lied about sexual abuse." Because the trial turned on the jury's assessment of the complainant's credibility, the improperly admitted testimony "likely affected the jury's ultimate decision."^[14]

A number is not required for testimony to be improper. In People v Sattler-VanWagoner (2024), the Court of Appeals said an expert's statement that false reports are "statistically very rare," though lacking a numeric value, "was essentially the statistical vouching described in Thorpe."^[15] This guide makes no claim about how often reports are true or false; the point of these cases is that the question in a trial is what happened in that case, which is for the jury.

People v Harbison: no "diagnosis" without physical findings

Thorpe was decided together with a second case. The MJI Evidence Benchbook names it: "In People v Harbison, the case consolidated with Thorpe, the Michigan Supreme Court considered 'the admissibility of expert testimony from an examining physician that "diagnosed" the complainant with "probable pediatric sexual abuse" despite not having made any physical findings of sexual abuse to support that conclusion.'"^[16] The published citation for both is 504 Mich 230.^[16]

The opinion states this as its holding in Harbison.^[6] The rule, as the Sexual Assault Benchbook quotes it: "examining physicians cannot testify that a complainant has been sexually assaulted or has been diagnosed with sexual abuse without physical evidence that corroborates the complainant's account of sexual assault or abuse because such testimony vouches for the complainant's veracity and improperly interferes with the role of the jury."^[4]

The Court's reasoning, again as quoted, was that testimony of "probable pediatric sexual abuse" based solely on the expert's view that the account was "clear, consistent, detailed and descriptive" is "nothing more than the doctor's opinion that the victim had told the truth," and a jury is "in just as good a position to evaluate the victim's testimony as" the doctor. Because there had been no objection at trial, the Court reviewed Harbison's claim for plain error; it found the error plain, found that it affected his substantial rights, and reversed.^[17][6]

The Court of Appeals has since described this as "a bright-line rule that an examining physician's opinion that a complainant was sexually abused is admissible only if supported by physical findings,"^[18] and has held that "'[p]ossible pediatric sexual abuse' is not significantly different from 'probable pediatric sexual abuse' in terms of the physician's endorsement of the accusation."^[19]

What an examining physician may say

Physicians are not barred from testifying. The benchbook quotes older Michigan cases for the general rule: an examining physician is a proper witness so long as the testimony may assist the jury on "penetration itself" or "penetration against the will of the victim," but the physician "may not testify that [a] complainant was raped by the defendant on the alleged date" or give an opinion on the complainant's veracity.^[20]

The same opinion keeps room for opinions that rest on the examination, restating the Court's 1986 decision in People v Smith.^[6] An examining physician, "if qualified by experience and training relative to treatment of sexual assault complainants, can opine with respect to whether a complainant had been sexually assaulted when the opinion is based on physical findings and the complainant's medical history."^[21] The benchbook gives Court of Appeals examples in which an opinion was properly admitted because it rested on objective facts from the medical examination, or was confined to whether penetration occurred without addressing place, time or by whom.^[22]

What a patient told the physician is a separate hearsay question, covered in statements to doctors and SANE nurses.

Sexual assault nurse examiners

A sexual assault nurse examiner (SANE) is described in the benchbook as a registered nurse specially trained to provide care to sexual assault patients, who conducts medical forensic examinations and can serve as an expert witness.^[23] The Court of Appeals has said MRE 702 "does not require that an expert be certified by the state in the particular area in which the expert is qualified," so a licensed nurse may give expert testimony without yet holding SANE certification.^[23]

In the same case, People v Brown, a nurse's testimony "regarding the lack of injury in most sexual assault cases" was held properly admitted "because it was based on [the nurse's] specialized knowledge and assisted the jury in understanding the evidence in this case."^[24] The examination a SANE performs is described in the sexual assault forensic exam.

Police and forensic interviewers

The limits are not confined to witnesses formally qualified as experts. In People v Musser the Michigan Supreme Court quoted the concern that "courts should be particularly insistent in protecting innocent defendants in child sexual abuse cases" given "the concerns of suggestibility and the prejudicial effect an expert's testimony may have on a jury."^[25] The benchbook reports the holding that a detective who was not qualified as an expert was still subject to the same limitations.^[26]

How an interview was conducted can itself be an issue at trial. The Evidence Benchbook quotes a 2025 Court of Appeals decision: "Frequently, the process and protocol by which a complainant was interviewed will be directly relevant to an issue in dispute."^[27] The protocol is explained in forensic interviews of children.

What the jury is told

When behavioral expert testimony is admitted, M Crim JI 20.29 limits its use. The instruction says the evidence "cannot be used to show that the crime charged here was committed or that the defendant committed it. Nor can it be considered an opinion by [name expert] that [name complainant] is telling the truth."^[5]

Deciding which witnesses to believe remains the jury's job.^[28] How jurors are instructed on credibility and on the prosecutor's burden is covered in cases without other witnesses; the hearsay rule for a young child's first statement is in the tender-years rule; and courtroom accommodations are in child witnesses in Michigan courts.