A former Pennsylvania veterinary technician-turned-nurse and suspected serial killer who lost 17 patients and injured more, had a "murderous rage" and could have been a "budding serial killer" before she got her nursing license, according to a former detective and a criminal profiler who have followed the case and others like it.

Heather Irene Pressdee was first accused of injecting three patients with insulin, killing two and injuring a third in November 2022 and later claiming she "felt bad for their quality of life," according to a criminal complaint. Authorities tacked on more than a dozen new charges Friday. 

Between 2018 and her arrest in May, she resigned or was fired from 11 medical sites amid complaints of abusive behavior toward patients and colleagues, according to a police affidavit. Beyond that, however, she is now accused of overdosing patients on insulin, including some who were not diabetic and shouldn't be injected with the drug.

PENNSYLVANIA NURSE ACCUSED OF KILLING 2 PATIENTS, INJURING 3RD ‘FELT BAD FOR THEIR QUALITY OF LIFE’: POLICE

Heather Pressdee inset over insulin syringe

Suspected serial killer and Pennsylvania nurse Heather Pressdee is accused of injecting patients with potentially lethal doses of insulin. (iStock I Inset: Heather Pressdee/Facebook)

The case has drawn comparisons to the murders committed by Charles Cullen, a New Jersey nurse-turned-serial killer whose insulin poisoning attacks led to the movie "The Good Nurse" starring Jessica Chastain and Eddie Redmayne, John Kelly said.

Pressdee even caught the attention of the detective who worked that case, Tim Braun, played in the movie by Noah Emmerich. He told Fox News Digital Friday Pressdee may have already been a budding killer before she joined the health care industry.

"She experimented basically for years before she moved on to humans."

— Tim Braun, former detective who investigated similar series of murders

"She’s only been a nurse for five years. Before that, she was a vet tech, and one of her primary responsibilities was administering anesthesia to animals and also euthanizing animals," he told Fox News Digital. "She experimented basically for years before she moved on to humans."

Through a search warrant on Pressdee's cellphone, police said they uncovered a Christmas Day text message to her mother in which she wrote, "I can't with this lady. She's going to get pillow therapy."

Two days later, an 85-year-old woman under her care died, and police say Pressdee eventually admitted to giving her 60 doses of short-acting insulin. Court documents allege Pressdee has admitted to 19 similar incidents.

Heather Pressdee selfie

An affidavit alleges Pressdee gave alleged victims lethal doses of insulin, a hormone used to reduce blood-sugar levels typically given to patients with diabetes. (Facebook/Heather Pressdee)

She also allegedly timed the doses so that victims "would expire" before the next shift change, reducing the chance she'd be exposed, according to police. Patients who looked like they'd survive would get another dose. In at least one case, she searched the internet for the obituary of one of her alleged victims.

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Forced insulin overdosing is a particularly painful way to die, Braun said, arguing that excuses raised by both Cullen and Pressdee involving "mercy" were total fabrications.

"Insulin, I came to learn, is not a pleasant way to go," he told Fox News Digital.

Charles Cullen in court

Charles Cullen, 43, from Bethlehem, Pa., in a courtroom Dec. 15, 2003, in Somerville, N.J. Cullen admitted to killing 40 terminally ill patients in nine hospitals and a nursing home.  (Getty Images)

Braun and criminal profiler Kelly, who has interviewed numerous serial killers, both predicted there would be more victims after Pressdee's arrest earlier this year in two insulin-related deaths and another patient's illness.

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"The question here is the why?" Kelly, told Fox News Digital.

Many serial killers begin by torturing or abusing animals, he said, and become desensitized over time. That could have happened for Pressdee in a "clinical setting," the vet's office.

"Putting animals to sleep and then, you know, that helped her put bigger animals to sleep, like humans, just like with other serial killers," he said. "It gets easier."

Heather Pressdee mugshot

Heather Pressdee, 40, of Natrona Heights, is facing charges of homicide, attempted murder, aggravated assault, neglect of a care-dependent person and reckless endangerment. (Pennsylvania Attorney General's office)

Now that allegations of additional victims have been made public, including the text messages, he says Pressdee has shown a "murderous rage." Other texts from her phone allegedly included death threats for fast-food workers, co-workers and other people.

"I'm gonna get fired tonight," one alleged message states. "If this [sic] says excuse me one more time because she can't remember my name she may die."

One notable difference between the Pressdee and Cullen cases is the paper trail, Braun said. Cullen kept the killing secret, and close friends and family had no idea, while Pressdee allegedly texted her mother repeatedly about the desire to kill people.

"Cullen, he had a silent rage," Braun said. "She's communicating with others in this fashion, but he didn't. The closest people around him had no idea of the stuff he was doing."

"A couple of serial killers have told me there’s no higher high than playing God."

— John Kelly, criminal profiler and president of STALK Inc.

Kelly called excerpts from the text messages "homicidal delusions."

On Friday, Pennsylvania prosecutors announced two more murder charges, 17 new counts of attempted murder and 19 counts of neglecting a care-dependent person. The charges don't fully illustrate the damage, authorities said.

They only charged murder on four cases in which they believed they had enough physical evidence, but a total of 17 patients died while under Pressdee's care.

"You gotta believe that there's more victims," Kelly said.

Read the complaint (Mobile users go here)

Braun agreed, saying Cullen was addicted to killing.

"Cullen and probably most other serial-type killers, it becomes an addiction. And Cullen told us he couldn’t stop," he said. "If we hadn’t stopped him, he would’ve continued to kill."

The latest allegations involve five centers between 2020 and this year — Concordia at Rebecca Residence, Belair Healthcare and Rehabilitation (Guardian), Quality Life Services Chicora, Premier Armstrong Rehabilitation and Nursing Center and Sunnyview Rehabilitation and Nursing Center.

"It is hard to comprehend how a nurse, trusted to care for her patients, could choose to deliberately and systematically harm them," Pennsylvania Attorney General Michelle Henry said in a statement. "The damage done to the victims and their loved ones cannot be overstated. Every person in a medical or care facility should feel safe and cared for, and my office will work tirelessly to hold the defendant accountable for her crimes and protect care-dependent Pennsylvanians from future harm."

"It is hard to comprehend how a nurse, trusted to care for her patients, could choose to deliberately and systematically harm them."

— Pennsylvania Attorney General Michelle Henry

The victims ranged in age from 43 to 104. Authorities are asking anyone else with information on Pressdee's activities to call the tip line at 888-538-8541.

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The nurse is being held without bail at Butler County Prison.

"A couple of serial killers have told me there’s no higher high than playing God," Kelly said. "They have the choice over whether they live or die at that point in time, and that’s the gratification that could be soothing the anger in a way."

For them, he said, it's about power and control over helpless victims.