In what’s “believed to be the longest murder trial in the U.K.,” according to the BBC, former nurse Lucy Letby was found guilty of killing seven infants in a neonatal unit, and attempting to kill six other infants, on Friday.

This verdict makes her “the U.K.’s most prolific child serial killer in modern times,” BBC added.

The Washington Post reported, “During the trial, prosecutors alleged that Letby killed five boys and two girls and attempted to kill another five boys and five girls in the hospital’s neonatal unit by poisoning them with insulin, injecting air into their veins or overfeeding them with milk.”

The murders occurred between 2015 and 2016, while Letby worked at the Countess of Chester hospital, according to Reuters.

CBS News reported that an investigation was launched in 2017 after the spike in infant deaths.

“Letby was arrested three times in connection with the deaths before she was charged in November 2020,” with her defense lawyer saying there wasn’t sufficient evidence to prove Letby the culprit.

After the 33-year-old’s arrest in 2018, police found a handwritten note that read, “I killed them on purpose because I’m not good enough to care for them,” “I am a horrible evil person,” and “I AM EVIL I DID THIS,” Reuters said.

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This court artist drawing by Elizabeth Cook from Aug. 11, 2023, shows of nurse Lucy Letby at Manchester Crown Court in Manchester, England. A neonatal nurse in a British hospital has been found guilty of killing seven babies and trying to kill six others. Letby was charged with murder in the deaths of five baby boys and two girls, and the attempted murder of five boys and five girls, when she worked at the Countess of Chester Hospital in northwest England between 2015 and 2016. | Elizabeth Cook, Associated Press

After the first two sets of guilty verdicts were declared on Aug. 8 and Aug. 11, “the jury was unable to reach verdicts on six further attempted murder charges relating to five babies,” the BBC said.

In a statement, Nicola Evans, detective chief inspector for the Cheshire Constabulary, said, “Today is not a time for celebration. There are no winners in this case.”

“Our focus right now is very much on the families of the babies,” Evans said, per the Post. “The compassion and strength shown by the parents — and wider family members — has been overwhelming.”

Of the children who survived the attacks are a girl and boy, ages 8 and 7, who live with severe brain damage due to the injury inflicted by Letby, according to The Guardian.

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Pascale Jones of Britain’s Crown Prosecution Service said, “Lucy Letby sought to deceive her colleagues and pass off the harm she caused as nothing more than a worsening of each baby’s existing vulnerability,” per CNN.

The families of the infants who died said in a joint statement on Friday, “Justice has been served and the nurse who should have been caring for our babies has been found guilty of harming them.

“But this justice will not take away from the extreme hurt, anger and distress that we have all had to experience. ... We are heartbroken, devastated, angry and feel numb,” per CNN.

The trial started in October 2022 and “sentencing of Letby for all guilty charges will be at 10 a.m. local time on Monday,” Aug. 21, according to the BBC.