PIERRE, S.D. (KELO) — The defense for a Wagner mother accused of second-degree murder in the death of her three-year-old daughter while they were staying with another family won’t be able at her upcoming trial to use an expert’s testimony suggesting another boy had the capacity to have killed the girl based on the boy’s previous behavior.

The South Dakota Supreme Court publicly released the unanimous decision Thursday. The justices said the defendant, Amanda Rose Hernandez, can’t use the opinion of a clinical psychologist specializing in child behavior, Dr. Thomas Stokes, to suggest that the 10-year-old son of the other family could have been the killer instead.

That is because, according to the state’s high court, the psychologist’s testimony would violate state laws regarding what’s known as propensity evidence that “endorses the premise that a person acted in a particular way because of an alleged trait or history.”

Hernandez’s attorney, Timothy Whalen of Lake Andes, wanted the psychologist to say that N.M., the 10-year-old son of the other family, could have been responsible for the death of Hernandez’s daughter, based on the boy’s aggressive conduct and actions toward other children in the community.

Circuit Judge Bruce Anderson said the psychologist could present the testimony. State prosecutors appealed to the Supreme Court. The five justices agreed that Judge Anderson erred. Justice Patricia DeVaney authored the high court’s decision.

“The rules of evidence, including those which govern the admissibility of expert opinions, are designed to avoid placing misleading, confusing, unreliable, or inaccurate evidence before a jury,” Justice DeVaney wrote.

She added, “Dr. Stokes’s opinion that N.M. has the capacity to commit the crime at issue skirts the requirements for admissibility under these evidentiary rules. His opinion testimony is pure propensity evidence of the sort that is expressly forbidden under SDCL 19-19-404. Dr. Stokes relies on N.M.’s history, character traits, and particularly, his prior acts, to draw the conclusion that N.M. would be capable of fatally injuring A.H. Thus, his opinion is, in essence, that because N.M. has previously acted aggressively in certain circumstances, it is plausible that he acted in conformity with this previous conduct by killing A.H.”

Justice DeVaney said there also were multiple other problems with Judge Anderson’s determination to admit the psychologist’s testimony.