'Trusted friend' of family accused of killing baby while parents were at hospital with his twin brother

A baby was allegedly killed by a 'trusted friend' of a family while she was babysitting.

Nicole Virzi, 29, was arrested on suspicion of the murder of six-week old Leon Katz at his home in Pittsburgh.

As per documents obtained by NBC 7, Virzi is charged with homicide, two counts of child endangerment, and three counts of aggravated assault.

The 29-year-old has been described as a 'trusted friend' of Leon's parents Ethan Katz and Savannah Roberts.

Leo has tragically died at six weeks old. (GoFundMe)

Police claim that Virzi allegedly killed the infant while his parents were at the hospital with his twin brother, who they allege Virzi also assaulted.

She told police she had gone into the kitchen to get Leon a bottle when she suddenly heard screaming.

Upon returning, Virzi claimed the baby had fallen out of his bouncer chair and called 911 at 11:15pm local time. She told dispatchers the baby was conscious but having trouble breathing.

Virzi told police that she found Leon on the ground with a 'large bump on his head'.

He was rushed to hospital but tragically passed away.

Nicole Virzi. (Allegheny County Jail)

A CT scan later determined that Leon suffered a skull fracture, along with multiple brain bleeds.

"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 investigators.

Investigators added Virzi could not provide a 'plausible explanation' for the injuries.

Virzi has denied any wrongdoing and her lawyer has maintained her innocence.

"Our client denies these allegations. She is a loving person and a friend to these people and would never harm anyone's child, let alone theirs,' her attorney, David Shrager, told Pittsburgh's WTAE.

Ethan and Savanna pictured with with Leon and his twin brother. (GoFundMe)

A GoFundMe page set up for the devastated parents has provided more detail, with it saying that Leon was 'tragically killed under horrific circumstances' and that a 'trusted family friend' has been arrested.

The GoFundMe reads: "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 and the parents’ first wedding anniversary.

"While financial support is crucial, Ethan, Savannah, and Ari are profoundly grateful for the outpouring of love they have received. Your messages of support mean the world to them as they begin to heal from this unimaginable loss.

"Thank you for keeping the Katz family in your thoughts and prayers during this incredibly challenging journey."

The suspect is being held without bail at the Allegheny County Jail.

Virzi now faces a preliminary hearing on June 28.