Doctoral student is accused of killing a child she was caring for a friend and injuring his twin

A California student killed her friend's 6-week-old baby and attacked his twin brother at her parents' home in Pittsburgh, police said.

Nicole Virzi, 29, was babysitting the little twins on Saturday. The University of California-San Diego psychology doctoral student, a longtime family friend, told parents she noticed scratches on one twin's face, stomach and genitals. The San Diego Union-Tribune Reports.

The parents quickly rushed the newborn to the hospital and left the student alone to look after his brother Leon Katz. That evening, the baby suffered multiple skull fractures that led to his death, authorities say.

Virzi was charged with murder, aggravated assault and endangering the welfare of a child. The parents said they did nothing wrong and did not see any of the newborns injured except by the babysitter Union-Tribune Reports.

Virzi told police she put Katz in a high chair that night but forgot to strap him in before leaving the room to get a bottle, the newspaper said Union-Tribune. When she returned, the 6-week-old child was lying on the floor and had a large bump on her head, Virzi said. Then she called 911.

Paramedics took Katz to a local hospital, where he died Sunday from blunt force trauma to the head. According to CBS Pittsburgh, doctors said the injuries were “due to child abuse.”

According to police, Katz did not provide a “plausible explanation” for the infant’s serious injuries.

Defense attorney David Shrager told CBS Pittsburgh that Katz's death was “a terrible thing” but that doesn't mean “anyone is guilty.”

“Our client denies these allegations,” Shrager said, according to local news outlet WTAE. “She is a loving person and a friend to these people and would never harm anyone's child, let alone hers.”

Accordingly, Virzi pleaded not guilty to all charges Union-Tribune. She is being held in the Allegheny County Jail after her bail was denied.

Virzi is a doctoral candidate in a clinical psychology program run jointly by San Diego State University and the University of California-San Diego. According to San Diego State University's website, its research areas include behavioral medicine, women's health and eating disorders.