PH. D. STUDENT SPECIALIZING IN DEPRESSION CHARGED WITH KILLING FRIEND'S INFANT WHILE BABYSITTING TWINS. (PHOTO).

 Ph.D. student specializing in depression charged with killing friend’s infant while babysitting twins

Two parents put their twin babies' lives in the hands of a "trusted family friend," who allegedly killed one of the boys and abused the other, according to prosecutors.

Nicole Virzi, a fifth-year Ph.D. student specializing in research about depression's effect on human behavior, babysat 6-week-old twin boys, Leon and Ari Katz, on June 16. 

That's the day Leon died. Virzi said he fell from his bouncer chair after she woke up from a nap and walked away to get a bottle.

But doctors who examined the baby's injuries found a skull fracture on the left side of his head and several brain bleeds "consistent with having been sustained as a result of child abuse," WTAE reported. 

Virzi, 29, was arrested by police near Pittsburgh, Pennsylvania, where she was babysitting the kids, and charged with homicide, three counts of aggravated assault and two counts of child endangerment. 

There were allegedly signs of abuse on the other baby, too, according to prosecutors. 

She pleaded not guilty, and maintains her innocence, her lawyer, David Shrager, said.

"There are extremely disturbing allegations," Shrager told Fox News Digital, "and she denies any intentional behavior."

Virzi is the daughter of a respected Manhattan cardiologist and was a few steps from the finish line to getting her Ph.D., according to Shrager. 

She has no criminal history, is backed by "a loving and supportive family," and is a "close family friend of the deceased child's parents and has a long relationship with them," he said. 

Just three days before the alleged homicide, Virzi discussed her new research paper in a video on Heart and Mind Journal Office's X page, which has since been taken down. 

Heart and Mind Journal Office couldn't be reached for comment. 

The doctors' medical exam on baby Leon details disturbing wounds. 

"The injuries sustained by both (twins are) consistent with having been sustained as a result of child abuse, as these are inflicted injuries that are not natural and not accidental," a doctor told detectives, according to a report by WTAE, based on the criminal complaint.

The baby's death was ruled a homicide. Virzi is currently being held in the Allegheny County Jail in Pennsylvania. 

"Leon Katz, a beautiful and healthy six-week old baby boy, was tragically killed under horrific circumstances," according to a GoFundMe set up on behalf of his parents, Savannah and Ethan Katz.

"Leon will always be remembered as a happy, smiley, goofy baby boy. His untimely and tragic death has deeply impacted the Pittsburgh community, occurring on Ethan's first Father's Day."

Virzi wrote in her bio on the San Diego State University/UC San Diego Joint Doctoral Program in Clinical Psychology's website that her research "aims to explore the complex interplay between psychological factors – such as depression, stress, negative affect, and trauma – and critical health outcomes and behaviors – such as metabolic syndrome, heart disease, obesity, eating behavior, and exercise."

"I am particularly interested in exploring these relationships within female and trauma-exposed populations," Virzi wrote in her bio. 

"By concentrating on these relationships, my research aims to shed light on the unique challenges and opportunities for intervention within these vulnerable groups."