The heartbreaking story of a woman who killed her six-week-old daughter by putting her in a microwave oven took a new twist when a California Court of Appeal reversed her conviction due to the improper admission of medical evidence to explain her tragic actions.

Was defendant Ka Yang’s behavior due to epilepsy, or was it a result of postpartum depression? Attorneys for the 29-year-old defendant presented evidence of her history of seizures, while the prosecution presented expert witnesses who attributed the murder to “baby blues,” or a common disorder after childbirth that can cause mood swings, anxiety, and insomnia.

Acting Presiding Justice Elena Duarte of the Third Appeal District of the State of California, called this “an excruciatingly tragic case.” She ruled on the defendant’s appeal on July 28 when she reversed Yang’s first-degree murder conviction. She wrote that the expert testimony about postpartum depression was not harmless error and was improperly admitted because it included medical records not directly related to relevant medical issues. Duarte wrote, “The issue was and needed to remain whether the killing was the product of the seizure disorder.”

Yang was the mother of four children, three boys and Mirabelle, her new daughter. The jury heard undisputed evidence about the events that led to the baby’s death in 2011. One afternoon, between 1 and 2 p.m., while alone with Mirabelle, Yang placed her in a microwave oven and turned on the power for several minutes. When first responders arrived at her home, she could only say that she didn’t know what happened. During the trial, they admitted that they “breached protocol” by failing to assess Yang’s medical condition or take her to a hospital. Mirabelle was pronounced dead at 2:33 p.m.

Later that day, Yang was interviewed by law enforcement and said she thought she had experienced a seizure, because she recalled seeing a flash of light, then awoke with Mirabelle lying next to her, “red in the face, stiff, and not breathing.” She had suffered from epilepsy since she was 13 or 14, and told officers that she had bitten her tongue and wet herself. She thought the baby’s death was the result of her unconscious actions, during which she might have dropped Mirabelle on a space heater.

A detective who interviewed her the day of the baby’s death disputed her report. He said that “he did not see blood or a fresh wound on defendant’s tongue, did not smell urine, and did not notice that defendant’s pants were wet.” A pacifier was found in the microwave. An autopsy showed that Mirabelle “died of thermal injuries resulting from overexposure to microwave radiation (up to five minutes) in a microwave oven.”

Yang was charged with first-degree murder and assault on a child and her case went to trial in August 2015. In December, she was sentenced to 25-years-to-life in prison, plus one year because the microwave was classified as a weapon-use enhancement. An appeal from the verdict of the Sacramento County Superior Court followed.

During the trial, prosecutors argued that there was a different explanation than Yang’s epilepsy—postpartum depression. The appeals court, however, found that their argument, supported by experts, was improperly admitted, and based on privileged medical records and testimony from Mirabelle’s pediatrician who did not tell the jury that Yang “screened negative” for the disorder. Yet, the prosecution relied on the tainted evidence to explain Yang’s behavior and to theorize that hallucinations related to “postpartum psychosis” caused her conduct.

At the trial, many witnesses including Yang’s brother, mother and husband, agreed that the defendant was a loving mother who cherished her new daughter. Her husband was a long-haul trucker often away from home for two weeks at a time, and on the job the day of Mirabelle’s death. He spoke to her the morning of the tragedy and reported that she did not complain of being stressed, overworked, or frustrated.

Photo Source: Baby Mirabelle (CBS/DailyMail) Relatives also testified about the hundreds of seizures Yang experienced that began since she was a young teen. Seizures caused her to fall down, become “weak, disoriented, confused or exhausted” and lose consciousness. Although she took medication, Yang said it did not help. There was also conflicting testimony about whether she told witnesses that she hallucinated and saw black shadows, spirits and other visual and auditory hallucinations that could have been related to her Huang culture.

The battle of the expert witnesses took place throughout the trial. Yang’s experts explained epilepsy and opined that “it was possible that defendant put Mirabelle in the microwave either during a complex partial seizure or while in a postictal state.” Another expert, originally asked by the prosecution to evaluate the case, said they “should not prosecute for murder. Enough probability exists that [defendant] may have had a seizure.”

The reason for the appeals court’s reversal of the murder verdict relates to the expert testimony of prosecution witnesses. Even though the trial court had ruled that “defendant’s psychological records were privileged,” the prosecutor announced that he had reviewed them prior to cross-examination of one of Yang’s expert witnesses. The prosecutor sought and received permission to “go into the psych records” including key testimony by Dr. Angela Vickers, Mirabelle’s pediatrician, who gave a lengthy explanation of postpartum depression, although she had “no special training in psychiatry or psychology and was admittedly not qualified to render an opinion regarding postpartum depression or psychosis.

Vickers also failed to testify that she saw any actual evidence of postpartum disorders in Yang, especially since she actually screened her and found her to be “negative for postpartum disorders after Mirabelle’s birth.” Instead, her testimony was full of descriptions of generalized “risk factors” and statistics.

The prosecutor’s closing argument still highlighted evidence that “supported the finding that the defendant suffered from postpartum psychosis” and urged the jury to ignore the fact that Yang was never diagnosed with any postpartum mental disorder.

After reviewing key components of the trial, the appellate court agreed “the trial court abused its discretion by admitting the challenged testimony.” The trial court had improperly admitted evidence of diminished capacity; that evidence of postpartum depression is not proper “motive” evidence; that the risk factor evidence constituted a “criminal profile”; and that the testimony contained improper statistical evidence.”

Other motives, specifically postpartum depression, should never have been discussed at trial. Thus, Duarte wrote, “viewed as a whole, the prosecution’s purported evidence of undiagnosed postpartum psychosis was weak and speculative, based almost exclusively on the strained assertion that defendant’s belief in spirits and use of such supernatural terms in reference to her seizures, her dreams, and her statements about what other people told her amounted to evidence of psychosis. The testimony was unsupported by sufficient factual bases.” All these evidentiary errors, Duarte concluded, amount to “cumulative prejudicial error, resulting in a miscarriage of justice and depriving defendant of a fair trial.”