"She wanted to take him to a mental hospital," testified Lizeth D., whose last name was not used in court.
Her mother, Veronica Aguilar, is accused of neglect and murder for allegedly hiding Yonatan in a closet for three years as he wasted away.
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At the time of death, the 11-year-old boy measured 46 inches, weighed 34 pounds and had an ulcer on his nose that was so deep that the cartilage was exposed.
Lizeth testified she had no memory of seeing Yonatan in an alarming condition or sleeping in a closet. The judge later called that testimony not credible.
Lizeth revealed a sharper memory of Yonatan's behavior. She recalled that he once ate ants, urinated on her belongings, attacked a classmate and was so aggressive at home that Lizeth slept in an outdoor shack.
She expressed no sympathy about his death.
"Are you happy that he is dead," asked Deputy D.A. Lisa Kassabian.
"No," Lizeth replied.
"Are you sad that he is dead," asked Kassabian.
"No," Lizeth responded.
When LAPD questioned Aguilar about the death in August 2016, she said Yonatan had been trouble since he was in the womb.
"On several occasions during the interview she described Yonatan to be pure evil," testified L.A. Police Detective Sandra Platero.
A doctor testified that the boy's behavior could have been rooted in an extremely rare brain defect.
"This diagnosis is almost impossible to make by most physicians," testified Dr. Marvin Pietruszka, a witness for the defense.
The prosecution alleges that Aguilar sedated Yonatan with a liquid cold medicine and deprived him of food, water and medical care.
Testimony revealed that for three years, Aguilar told her husband that she had sent Yonatan to Mexico where he was "doing fine."
At the request of the prosecutor, the judge added a special circumstance allegation of torture.
Aguilar will face trial on all charges and with the added allegation could potentially face the death penalty if convicted.