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Murder Conviction for Mother Reversed Due Erred Expert Testimony

California v. Yang Court: California Courts of Appeal, Docket: C080978 (Third Appellate District), Opinion Date: July 28, 2021. A mother of four young children was found guilty by jury of first degree murder and assault on a child resulting in death, after she killed her youngest child and only daughter. There was no dispute defendant Ka Yang, while alone with her baby Mirabelle, placed the baby in a microwave oven and turned it on. These actions killed the baby. Defendant told her family and first responders that she did not know how the baby was injured, but she consistently spoke of having suffered a seizure, and guessed that the baby had been injured when dropped on a nearby heater while defendant was incapacitated. Defendant's defense at trial, supported in part by expert testimony, was that she killed her daughter while unconscious due to an epileptic seizure. The prosecution countered defendant’s claim of unconsciousness with expert testimony of its own (and medical records), after an inadvertent disclosure by the trial court allowed the prosecutor to discern these records’ contents midtrial and secure their admission on that basis. Although defendant had not been diagnosed with any postpartum mental disorder, and Mirabelle’s pediatrician testified defendant had screened negative for any such disorder, the prosecution relied on this evidence to theorize that defendant was motivated to kill her daughter by hallucinations related to undiagnosed postpartum psychosis. The Court of Appeal concluded the trial court abused its discretion by allowing expert testimony regarding postpartum mental disorders without sufficient factual basis and by subsequently admitting into evidence defendant’s psychological records not directly related to any mental condition she had put at issue. The Court could not conclude these errors were harmless when considered together, thus it reversed the judgment in its entirety.

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