A neonatal nurse in the U.K. who allegedly murdered seven babies and attempted to kill 10 more wrote notes reading, "I am evil" and "I killed them on purpose because I'm not good enough," according to the prosecution.

Lucy Letby, 32, who worked in the neonatal unit of the Countess of Chester Hospital, left handwritten notes in her home that police found when they searched it in 2018, prosecutor Nick Johnson told the Manchester Crown Court jury, according to the BBC.

Earlier this week, Johnson argued that Letby was a "constant, malevolent presence" in the neonatal unit. Of the babies Letby allegedly murdered or attempted to murder between 2015 and 2016, the prosecution said she injected some with insulin or milk, while another she injected with air. She allegedly attempted to kill one baby three times.

Neonatal nurse Lucy Letby

Neonatal nurse Lucy Letby, 32, is alleged to have murdered seven babies and attempted to kill 10 more. (SWNS)

"I don't deserve to live," read one of Letby's notes, which were projected onto a large TV screen for the courtroom to see. "I killed them on purpose because I'm not good enough to care for them. I am a horrible evil person."

One read in large capital letters: "I AM EVIL. I DID THIS."

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Johnson also said some notes contained "many protestations of innocence," such as one with the phrase, "I haven't done anything wrong, and they have no evidence so why have I had to hide away?"

Babies in a nursery

Stock image of newborn babies in a hospital nursery. (ER Productions Limited via Getty)

"Well, ladies and gentlemen, that in a nutshell is your task in this case," Johnson told the jury. "Whether or not she did these dreadful things is the decision you will have to make when you have heard all the evidence."

Ben Myers, a lawyer for Letby's defense, characterized the notes as expressions of "anguish not guilt."

Myers argued that "anyone with an ounce of human understanding" would perceive her notes as "the anguished outpouring of a young woman in fear and despair when she realizes the enormity of what is being said about her."

Police search Lucy Letby home

Cheshire Police in the U.K. search the home of Lucy Letby in 2018, when they found handwritten notes that were shown to jurors this week. (Peter Byrne/PA Images via Getty Images)

He pointed out how other messages in the notes say things such as "I'll never marry or have children" and "I haven't done anything wrong."

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Johnson told jurors this week that "a poisoner was at work" at the hospital, which he said had been marked by a "significant rise in the number of babies who were dying and in the number of serious catastrophic collapses" after January 2015, before which he said its rates of infant mortality were comparable to other busy hospitals.

Countess of Chester hospital

The maternity ward of the Countess of Chester Hospital in the U.K., where Letby worked and is alleged to have killed seven babies between 2015 and 2016. (Christopher Furlong/Getty Images)

Investigators found Letby was the "common denominator," and that the infant deaths aligned with her shifting work hours. 

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Letby pleaded not guilty to seven counts of murder and 15 counts of attempted murder Monday. Her trial is slated to last for up to six months.