A British nurse was found guilty Friday of murdering seven newborn babies and trying to murder six others at the hospital neonatal unit where she worked, becoming the UK’s most prolific killer of children.

Lucy Letby, 33, who has been on trial since last October, was accused of injecting her young victims, who were either sick or born prematurely, with air, overfeeding them milk, and poisoning them with insulin.

The jury at Manchester Crown Court in northern England reached all of its verdicts after deliberating for 22 days.

Letby was arrested following a string of baby deaths at the neonatal unit of the Countess of Chester Hospital in northwest England between June 2015 and June 2016.

Described by the prosecution as a “calculating” woman who used methods of killing that “didn’t leave much of a trace”, Letby repeatedly denied harming the children.

“Lucy Letby was entrusted to protect some of the most vulnerable babies. Little did those working alongside her know that there was a murderer in their midst,” Senior Crown Prosecutor Pascale Jones said in a statement.

“Time and again, she harmed babies in an environment that should have been safe for them and their families,” the prosecutor added, calling the killings “a complete betrayal of the trust placed in her”.

‘Playing God’

The court heard that colleagues raised concerns after noticing that Letby was on shift when each of the babies collapsed, with some of the newborns being attacked just as their parents left their cots.

Prosecutor Nick Johnson said Letby “gaslighted” her colleagues into believing the string of deaths were “just a run of bad luck”.

Letby’s final victims were two triplet boys, referred to in court as babies O and P.

Child O died shortly after Letby returned from a holiday in Ibiza in June 2016, while child P died a day after their sibling.

Letby was also said to have attempted to kill the third triplet, child Q, but the jury was unable to reach a verdict on the charge.