By 2-1, Colorado’s second-highest court on Thursday upheld a man’s child sex assault convictions despite an expert witness vouching for the credibility of the victims — which is typically improper.

A three-judge panel for the Court of Appeals agreed Gustavo Lopez “opened the door” to the problematic evidence by suggesting his child victims had been coached to implicate him in a crime. They also agreed a defendant who opens the door to otherwise-barred testimony is not entitled to a new trial if the goal is to give context to the jury about coaching.

However, the panel disagreed about how far it strayed from the established principle that witnesses may not testify about whether other witnesses are telling the truth.

Judge Elizabeth L. Harris, in the panel’s March 14 opinion, stressed that the green light to improper testimony only applies in “narrow” instances where a defendant “clearly intended to suggest” a child victim’s allegations are the product of coaching. In Lopez’s case, an expert appropriately countered the defense’s narrative by testifying she did not think adults had coached the victims on what to say.

“The testimony is not admissible under this exception any time the defendant challenges the child victim’s credibility,” Harris wrote for herself and Judge Lino S. Lipinsky de Orlov.

Judge Timothy J. Schutz dissented, believing the Court of Appeals was itself “opening the door” wider than it needed to. Although an expert witness, in his view, could properly describe the usual behaviors from a child who has been coached, the expert in Lopez’s case effectively told jurors they could believe the victims because there had been no coaching.

“In the typical case involving allegations of sex assault on a child, the defendant must either contest the veracity of the alleged victim or effectively confess,” Schutz wrote. “But the logical extension of a broad ‘opening the door’ rationale would permit an expert to opine whether the accusing witness was being truthful every time a defendant suggests that an accuser was coached.”

Lopez stood trial in Boulder County in 2019 for multiple child sex assault-related charges against three victims who were relatives of his. Jurors found him guilty and he received an indefinite prison sentence of at least 50 years.

There was no physical evidence of the crimes and the victims’ stories had many inconsistencies. Jurors also heard that two of the children wanted to live with their grandmother, who did not like Lopez.

During trial, the defense suggested family members can “influence” children into believing “something that’s not true.” Lopez’s attorneys also suggested the victims’ stories changed during the time spent with their grandmother.

Jurors heard testimony from Kim Grimm, a forensic interviewer who talked to two of the victims in recorded conversations. She described multiple tactics professionals use to discern if a child has been coached, including asking for details about their experience. The idea, Grimm said, is that people typically do not coach children on specific details about their environment, and it will be difficult for a coached child to recount that information.

At the end of Grimm’s testimony, the jury had a question for her: “In your expert opinion,” the question read, were the children’s behaviors “consistent with interviews where coaching was present?”

Over the defense’s objection, District Court Judge Andrew Hartman allowed her to answer. Grimm said she did not “feel like I saw huge red flags with that or anything.”

The Court of Appeals panel acknowledged witnesses may not testify about others’ truthfulness. In that vein, Grimm’s statement that she did not see signs of coaching effectively vouched for the victims’ credibility, Harris wrote.

At the same time, she continued, defendants may open the door to such testimony by “selectively presenting facts that, without being elaborated on or placed in context, create a misleading impression.” By pursuing a theory that the children’s grandmother had influenced their accounts, the defense triggered a need for Grimm to correct that impression.

“However, we reiterate that unless the defendant opens the door under the narrow circumstances we have described, the trial court commits error — potentially reversibly so — by allowing an expert to opine, even indirectly, about another witness’s credibility,” Harris wrote for the panel’s majority.

Schutz disputed that narrowness in his dissent. It is a jury’s role to determine the credibility of witnesses. But in sex assault cases, he emphasized, there is a “real risk” jurors may rely on an expert opinion when navigating through emotionally charged testimony.

“I disagree with the suggestion that the rule can or should be extended to permit a witness to testify that another witness was truthful on a particular occasion,” he wrote. “This provides the jury with nothing more than a conclusion on an issue that the jury is exclusively entrusted to make.”

The panel also rejected Lopez’s other grounds for appeal. First, it found Hartman did not need to respond “yes” when the jury sent him a note during deliberations asking whether they could return verdicts on some charges and hang on other charges. Second, the panel agreed Hartman acted appropriately when he asked one of the child victims a couple of questions in front of the jury to establish if the 10-year-old could tell the truth.

The case is People v. Lopez.