Moment glamorous PhD student Nicole Virzi - who now faces death penalty - is arrested outside her AirBnB the morning after she is alleged to have killed close friend's weeks-old child

The PhD student facing the death penalty for allegedly killing her friend's baby came across as the perfect guest at the Airbnb where she was staying in Pittsburgh.

Video exclusively obtained by DailyMail.com shows Nicole Virzi returning to her rental shortly before 1am June 16, appearing distraught and anxious as she struggled to unlock the door after she allegedly killed a six-week-old boy.

The following morning she is seen leaving the apartment and getting arrested outside. 

She had paid to stay there another two days. But early the next morning, the 29-year-old made a hasty exit. At 5:47am, she can be seen stepping back outside and making a phone call before police swooped in and took her into custody.

Nicole Virzi is accused of torturing six-week-old Leon Katz while watching him at the family's home in Pennsylvania 

Video exclusively obtained by DailyMail.com shows Nicole Virzi returning to her Airbnb rental in Pittsburgh shortly after midnight June 16, appearing distraught and anxious (pictured) as she struggled to unlock the door after she allegedly killed a six-week-old boy

Virzi allegedly said that she'd gone into the kitchen to get Leon (pictured) a bottle when she suddenly heard screaming. When she returned, she said the baby, left unstrapped, had fallen out of his bouncer chair

Virzi, who flew in from California to visit her friends, is now facing the prospect of the death penalty. She's accused of torturing six-week-old Leon Katz while watching him at the family's home. 

She is locked up without bail in a Pittsburgh jail, awaiting a a court appearance set for September 13.

Virzi had been staying at the Airbnb just a mile away from the Katz house.

Her profile on the app presents Nicole as a 'wonderful guest,' showing her smiling with a Hawaiian lei around her neck from a vacation.

'Graduate student who loves to travel!' her posting reads, followed by various hosts who sing her praises as 'very clean, respectful and kind.'

Virzi informed her host in Pittsburgh that she was living in Philadelphia and in town visiting some friends who live a few blocks away.

'I am looking forward to staying at your lovely apartment,' she wrote. 

'I do not need anything special, but I would like to let you know that I won't be checking in to the apartment until around 11:30 p.m. on Thursday, June 13. I will make sure to be quiet and respectful to others when I arrive. Thank you very much!'

The host told DailyMail.com on Friday that she didn't think twice about approving her guest.

'She had five reviews from the other hosts and five stars, was young, polite,' explained the owner, who asked not to be identified.

'It's so hard to believe that she could kill or be an abuser,' she continued. 'In the video when she's returning that night, she looked pretty sad and shocked. She didn't run away.'

Virzi is pictured leaving the Airbnb prior to the baby's death  before returning in the same outfit around midnight 

She can be seen stepping outside and making a phone call before police swooped in and took her into custody a few days later. She was taken to police headquarters for questioning, where she agreed to speak without a lawyer present

The Airbnb the PhD student stayed while visiting her friends in Pittsburgh 

In fact, Virzi wasn't living in Pennsylvania. She was on the West Coast finishing up her PhD at UC San Diego. She flew into town to visit her friends Savannah Roberts and Ethan Katz, parents to newborn twins.

Court papers described her as a 'trusted friend.'

Police, however, allege she fractured baby Leon's skull and caused several brain bleeds that were picked up by a CT scan. She's also accused of injuring Leon's twin brother Ari, who survived.

Court documents filed last week show the Allegheny County District Attorney's Office is seeking the death penalty against Virzi.

'The defendant committed the killing while in the perpetration of a felony,' the filing states. 'The offense was committed by means of torture.'

While being questioned by cops, Virzi allegedly said that she'd gone into the kitchen to get Leon a bottle when she suddenly heard screaming. When she returned, she said the baby, left unstrapped, had fallen out of his bouncer chair. She called 911 around 11:17pm on June 15, reporting that the baby was 'becoming non-responsive.'

Her Airbnb profile presents Nicole as a 'wonderful guest,' showing her smiling with a Hawaiian lei around her neck from a vacation

Virzi told the host she would be arrive late to the Airbnb when she checked in. The host told DailyMail.com on Friday that she didn't think twice about approving her guest. 'She had five reviews from the other hosts and five stars, was young, polite' 

At that time, the boy's parents were already at the hospital with their other twin son, Ari, who’d suffered an injury to his groin, along with scratches to his face and belly.

Virzi was the one who alerted the parents about the groin injury earlier in the day, court records state. Ari had blood in his diaper and swelling to his genitals, records show. Virzi allegedly sent a photo of the injury to the parents. 

Defense lawyer, David Shrager said  he has no idea what evidence prosecutors have to justify a homicide charge, much less a death penalty case

She claimed the boy also scratched his face when she was placing him in the car seat as he flailed his arms.

The Airbnb host sai she is still haunted by the unanswered questions in the case.

'Why did the parents leave her with the baby? Didn’t they question that the other one was left scratched?

‘Was it jealousy on Nicole’s end that her friend had babies?

‘It’s shocking, but at the same time, how do you know if people in real life are okay and that something won’t suddenly twist in their brain? 

Maybe Nicole’s choice of study was her trying to understand her own issues. It’s very sad and heartbreaking.’

Court papers state that after the 911 call for Leon, the dad, Ethan, rushed home, arriving just as paramedics pulled up. As Leon was transported to the hospital by ambulance, Ethan and Virzi drove to the hospital separately.

The accused killer didn't stay there long. The Airbnb surveillance footage shows Virzi arriving back at her rental at 12:53am on June 16  a little more than 90 minutes from the time paramedics were called.

Wearing a gray t-shirt and ripped jeans, her hair pulled back into a ponytail, she briskly walked up to the door, grim-faced. Clutching her cell phone in one hand, she used the other to punch in a passcode at the entrance to get inside. 

She struggled as she dialed the code, entering the wrong numbers in her first try.

As she headed in for the night, Leon was barely clinging to life. The baby was pronounced dead at 5:47am the morning of June 16.

Police were already on their way to Virzi's Airbnb at that moment. The video shows her stepping out of her rental at 5:45am. She reached for her phone and made a phone call. She then waited on the sidewalk.

Virzi is also accused of injuring Leon's twin brother Ari, who survived (pictured with Leon and his parents)

The Katz family home where the crime allegedly took place 

Virzi faces the death penalty. She has pleaded not guilty

Police cars pulled up at 5:50pm. Two officers hopped out and could be seen confronting her on the sidewalk, before leading her into the patrol car.

She was taken to police headquarters for questioning, where she agreed to speak without a lawyer present.

'Virzi was unable to provide any plausible explanation for the cause consistent with the extent of the injuries that Leon Katz sustained while in her care,' court papers state.

She has pleaded not guilty.

Speaking with DailyMail.com on Thursday, Virzi’s defense lawyer, David Shrager, said that since she was just formally arraigned last week, he still had no idea what evidence prosecutors have to justify a homicide charge, much less a death penalty case.

'My client has consistently maintained that nothing intentionally took place,' Shrager said.

He said that Virzi had been close friends for years with the mother, a fellow PhD student who is studying Clinical and Developmental Psychology at the University of Pittsburgh.

He said there’s ‘no rational reason’Virzi would want to harm the babies. He said his client has no prior criminal record and no mental issues he’s aware of.

She is a PhD student focusing on behavioral medicine. According to her UC San Diego bio, 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.'

'I am particularly interested in exploring these relationships within female and trauma-exposed populations. By concentrating on these relationships, my research aims to shed light on the unique challenges and opportunities for intervention within these vulnerable groups,' she said.

Shrager said his client is ‘maintaining a positive attitude, as much as she can under the circumstances,’ and that ‘her parents are also giving her 100 percent unwavering love and support.

‘She’s looking forward to sharing her truth at the appropriate time,’ the lawyer said.