Ringholz, a neuropsychologist from Baylor College of Medicine testifying for the defense, said his determination was based on research culled from her medical and family history and tests he conducted on the 37-year-old woman. The testimony of Ringholz is key to the defense, which must convince jurors Yates was insane when her children were drowned one by one on June 20. Prosecutors argue Yates was sane at the time of the killings.
Yates is on trial for two counts of capital murder. Prosecutors are seeking the death penalty in the deaths of 7-year-old Noah, 5-year-old John and 6-month-old Mary. Charges eventually could be filed in the deaths of Paul, 3, and Luke, 2.
On Monday, Ringholz said Yates's schizophrenia began during childhood and surfaced initially after giving birth to her first son, Noah, in 1994 when she considered grabbing a knife and stabbing the child.
Yates told him she felt Satan's presence shortly after Noah's birth and "heard Satan's voice tell her to pick up the knife and stab the child," Ringholz said. The symptoms of the schizophrenia didn't resurface until Yates' fourth son, Luke, was born in 1999. Medical records show that Yates attempted suicide twice that year.
Jurors were told the mental illness is characterized by a significant impairment in functioning and symptoms like delusions, hallucinations, incoherence and isolation. Defense attorney Wendell Odom asked Ringholz if Yates had ever been diagnosed with schizophrenia before. "Not that I'm aware of," Ringholz testified.
Earlier Monday, Dr. Melissa Ferguson, who interviewed the Houston mother in jail the day after her children were drowned, said Yates considered stabbing her five children but decided it was too bloody and that drowning was a better way to end their lives.