“The Jury Is the Lie Detector in the Courtroom”: The Rule Against Witness Vouching
Taylor R. Anderson, Boardman & Clark, LLP

In Wisconsin personal injury cases, as in other civil cases, the credibility of witnesses often plays a pivotal role in determining liability and damages. Plaintiffs may seek to bolster their case by having doctors, friends, or family members testify about the plaintiff’s character or, worse, suggest through their testimony that the plaintiff is inherently trustworthy. The rule against witness vouching is a critical safeguard in ensuring that such testimony does not unfairly influence the jury. For a civil defense attorney, the ability to effectively prevent improper vouching is essential in maintaining a fair trial and preventing plaintiffs from swaying the jury with subjective, non-evidentiary opinions about the truthfulness of their testimony.

The Haseltine rule, as it is called in Wisconsin, precludes witnesses from commenting on the credibility of other witnesses and whether they are telling the truth. This article will discuss the Haseltine rule against witness vouching, analyze key case law, and offer strategies for civil defense attorneys to combat improper vouching in personal injury cases, specifically when it involves testimony from doctors, family members, and friends.

I.              Legal Basis for the Rule Against Vouching

Wisconsin courts have long upheld the principle that witness credibility is solely the jury’s determination. Witnesses and attorneys may not offer personal opinions about the truthfulness of others because this would improperly influence the jury and usurp their role as factfinders.

This issue was first addressed in Wisconsin in the case of State v. Haseltine,[i] which establishes that a witness, such as an expert, cannot directly opine on another witness’ credibility. Relying on an Oregon Supreme Court case, the Haseltine court held that, “[n]o witness, expert or otherwise, should be permitted to give an opinion that another mentally and physically competent witness is telling the truth.”[ii] That case involved criminal charges related to sexual abuse and incest where the State offered the testimony of the victim’s psychologist to corroborate that the victim was telling the truth. The court found such testimony by the expert inadmissible and noted that “the jury is the lie detector in the courtroom.”[iii] 

The Haseltine rule is “rooted in the rules of evidence that say, ‘expert testimony must assist the trier of fact to understand the evidence or to determine a fact in issue.’ Expert testimony does not assist the factfinder if it conveys to the jury the expert’s own beliefs as to the veracity of another witness.’”[iv]

In State v. Romero,[v] the Wisconsin Supreme Court confirmed the holding from Haseltine and held that neither party may personally vouch for a witness’ credibility. The court explained that expressions of personal belief regarding a witness’ truthfulness encroach on the jury’s role, which is to independently assess whether a witness is credible based on the evidence. Although the Romero case involved a prosecutor’s conduct in a criminal trial, its reasoning applies equally to civil litigation, particularly personal injury trials, where doctors or experts may be called to testify about a plaintiff’s condition or credibility.

II.            Application of Vouching Rules in Personal Injury Cases 

In personal injury cases, plaintiffs often attempt to build their credibility by relying on the testimony of individuals who know them well, such as doctors, family members, or close friends. These witnesses, while sympathetic to the plaintiff, must stay within the bounds of permissible testimony. The rule against witness vouching prohibits these witnesses from offering opinions about whether the plaintiff is being truthful about claims of pain, suffering, or the circumstances surrounding the injury.

a.     Testimony From Doctors 

Doctors play a significant role in personal injury cases, particularly in establishing the extent of the plaintiff’s injuries and the prognosis for recovery. However, defense attorneys must remain vigilant when plaintiffs’ treating physicians are called to testify, as there is often a risk that the doctor will offer testimony that indirectly bolsters the plaintiff’s credibility.

For example, a doctor might testify that the plaintiff “has always been truthful” in reporting symptoms or that the doctor “believed” the patient about reported pain complaints. Such statements can come dangerously close to vouching for the plaintiff’s credibility. In State v. Snider,[vi] the court addressed a situation in which a detective testified that he found the victim’s story “credible.” The court found this improper because it amounted to a personal opinion about the truthfulness of another witness, a violation of the vouching rule. Defense attorneys should be prepared to challenge similar testimony from doctors, who may indirectly endorse plaintiffs’ truthfulness in discussing their symptoms.

Defense counsel should object to such testimony and, if necessary, file a motion in limine before trial to limit the scope of the doctor’s testimony. The doctor can and should testify about medical facts, diagnoses, and objective findings but should be precluded from expressing any opinion about whether the plaintiff’s subjective complaints of pain or suffering are truthful. There is often a fine line between the doctor testifying that a patient’s complaints were consistent with the objective findings the doctor observed and the doctor vouching for the patient. By raising the issue before trial with a motion in limine, the court can clarify that line before any testimony is given. The court’s decision in Haseltine provides clear authority for such objections, as it reaffirms that medical experts should not give opinions on credibility.

b.    Testimony From Friends and Family Members

It is common in personal injury cases for plaintiffs to call friends and family members to testify about their character, daily life, or how their injuries have impacted them. These witnesses, while offering important context about the plaintiff’s condition, must also be restricted from offering improper opinions about the plaintiff’s truthfulness. Statements like “She’s always been honest” or “He would never lie about this” are examples of impermissible vouching to which defense counsel should object.

In State v. Kuehl,[vii] the court addressed the impropriety of allowing a witness to testify about the credibility of another. The court ruled that such testimony encroaches on the jury’s role and could unfairly influence their assessment of the facts. Although Kuehl was a criminal case, its reasoning applies equally in personal injury cases where a plaintiff’s family or friends might try to indirectly vouch for the plaintiff’s truthfulness regarding the extent of claimed pain or limitations.

Defense counsel should remain watchful during such witnesses’ testimony, ready to object when a witness crosses the line into impermissible vouching. During depositions, defense attorneys should ask questions aimed at identifying any opinions or character assessments the plaintiff’s family or friends might offer at trial. This provides an opportunity to preemptively file a motion in limine to exclude any improper vouching testimony, ensuring that the jury’s focus remains on the objective facts of the case rather than subjective, biased character evaluations. In cases where the plaintiff has credibility issues of his or her own or is simply not a very good witness, counsel may use the plaintiff’s friends and family to bolster that credibility and provide corroboration of subjective complaints. In such circumstances, it can be easy for the witnesses to cross the line into vouching for their friend or family member, rather than providing testimony about what they actually observed.

III.          Strategic Use of Pretrial Motions and Objections 

One of the most effective tools a defense attorney can use to prevent improper vouching is the motion in limine. A well-crafted motion can help limit witness testimony before trial begins, preventing plaintiffs from improperly bolstering their credibility through vouching.

a.     Motions in Limine to Exclude Vouching Testimony

Before trial, defense counsel should file a motion in limine specifically targeting the types of improper vouching that are common in personal injury cases. The motion should cite relevant Wisconsin case law, such as Haseltine, Romero, and Kuehl, to argue that no witness should be permitted to offer an opinion about the truthfulness of the plaintiff’s statements regarding the claimed injuries or the accident itself.

For example, in a personal injury case where the plaintiff claims significant pain from an accident, the motion might request that the court prohibit the plaintiff’s treating physician from testifying about the plaintiff’s credibility concerning subjective complaints of pain beyond the doctor’s actual observations. The court should limit the doctor’s testimony to objective medical findings, diagnoses, and treatment plans. Similarly, the motion could seek to limit the testimony of friends and family members to observable facts rather than personal assurances of the plaintiff’s honesty.

b.    Objecting to Improper Vouching During Trial

In addition to pretrial motions, defense attorneys must be prepared to object to improper vouching during trial. Timing is critical when dealing with improper testimony, as failing to object immediately may result in the jury giving undue weight to impermissible statements. For example, if a family member testifies that the plaintiff “would never exaggerate about their injuries,” defense counsel should immediately object on the grounds that this is improper vouching and request a curative instruction from the judge. The judge may instruct the jury that credibility determinations are their responsibility and that they should disregard any testimony suggesting that the witness personally believes the plaintiff’s story. This swift action can neutralize the improper testimony before it taints the jury’s perception.

Raising an objection during trial is also important to preserve the issue for appeal because determinations by the circuit court regarding whether a witness is testifying to the credibility of another witness is a question of law that is reviewed de novo by the appellate courts and can be grounds for reversal.[viii]

IV.          Ethical Considerations for Civil Defense Attorneys 

In navigating the rule against vouching, civil defense attorneys must also remain cognizant of their ethical obligations. Wisconsin’s Rules of Professional Conduct prohibit attorneys from offering personal opinions on witness credibility.[ix] Defense attorneys must ensure that they do not cross this line when challenging witnesses on cross-examination or in closing arguments. 

For instance, in closing arguments, a defense attorney should avoid statements such as “I know the plaintiff is exaggerating,” which would constitute improper vouching or impeachment. Instead, the argument should focus on the evidence, inconsistencies in the plaintiff’s testimony, and any objective medical records that cast doubt on the plaintiff’s claims.

V.            Conclusion 

The rule against witness vouching is a crucial aspect of Wisconsin’s legal system, ensuring that juries make credibility determinations based on objective evidence rather than subjective opinions. For civil defense attorneys in personal injury cases, the rule provides both a shield against improper testimony from the plaintiff’s witnesses and a sword for challenging the credibility of those witnesses through permissible means. 

By utilizing pretrial motions, timely objections, and strategic cross-examinations, defense attorneys can effectively limit improper vouching and ensure that the jury’s decision is based on facts rather than personal opinions about the plaintiff’s truthfulness. Wisconsin case law, including the decisions in Haseltine, Romero, and Kuehl, provides a strong foundation for defending against vouching and maintaining the fairness of civil trials. 

Author Biography:

Taylor R. Anderson joined Boardman & Clark LLP in August 2023 and is an attorney in its litigation practice group after previously living in Las Vegas, Nevada. Taylor’s practice focuses on insurance defense, including personal injury, product liability, product damage, and insurance coverage. Prior to going into private practice, he clerked with a trial court judge in Eugene, Oregon. Taylor earned his bachelor’s degree from the University of Nevada, Reno, and his law degree from Willamette College of Law. He is admitted to practice in all Wisconsin state courts and both federal dis