Lucy Letby: How Authorities Zeroed in on British Nurse Accused of Murdering Infants in Neonatal Unit

Years after hospital staff grew suspicious about several unexplained infant deaths and unusual occurrences allegedly involving British nurse Lucy Letby, her murder trial is starting to wind down.

The shocking allegations, in which Letby, 33, is accused of murdering seven newborns and attempting to kill 10 more by injecting them with air, milk, or insulin at the Countess of Chester Hospital between 2015 and 2016, sent shockwaves throughout England and across the globe.

Letby has pleaded not guilty to 22 charges.

Since her trial commenced in October 2022, prosecutors have painted a picture of a severely disturbed woman hellbent on killing defenseless babies left in her care.

After a spike in the hospital's infant mortality rate too striking to ignore, here's how authorities finally zeroed in on the alleged baby killer.

2015: Doctor Grows Concerned Over 'Unexplained' Deaths

Citing a July 2016 report by the Royal College of Pediatrics and Child Health, in June 2015, a senior doctor at the Countess of Chester Hospital reportedly started to grow concerned over the surge in "unexplained" or "unexpected" deaths of newborns occurring in the neonatal unit, according to local news outlet the Hereford Times.

During Letby's trial, the BBC reports Dr. Ravi Jayaram told the court he brought the suspicious deaths and near-deaths to the attention of the hospital's senior director of nursing in the fall of 2015, but, he said, his concerns were overlooked.

Then, in February 2016, Jayaram said he alerted the hospital's medical director of the suspicious incidents surrounding Letby. Jayaram alleged he went on to request a meeting with the director but was ignored for three months.

"We were getting a reasonable amount of pressure from senior management at the hospital not to make a fuss," Jayaram testified, per the BBC.

Jayaram said he personally witnessed Letby standing over an infant with the baby's breathing tube dislodged. He alleged she stopped and watched as the baby's blood oxygen levels dropped at a dangerous rate, prompting him to intervene and administer CPR. The infant died three days later.

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Four months after the incident, Letby was removed from the hospital's neonatal ward and put on clerical duties, according to The Guardian.

Prosecutors said that hospital consultants suspected "that the deaths and life-threatening collapses of these 17 children were not medically explicable" and were the result of "the actions of Lucy Letby," the outlet reports.

According to the Hereford Times, numerous independent expert medical reviews of the circumstances surrounding the deaths were carried out before police got involved.

Police are called in 2017, Letby Arrested in 2018

In May 2017, the Times reports the Cheshire Constabulary launched its own investigation into the babies' deaths at the hospital, after the concerning allegations against Letby were brought to their attention.

In July 2018, after a 14-month probe, detectives had enough information to arrest Letby at her Cheshire, England, home, on the suspicion of murder.

After her 2018 arrest, Letby was released pending further investigation, reports say.

Through the collection of more evidence, police had probable cause to re-arrest her in June 2019 on suspicion of murder and attempted murders, but the former nurse bailed out once more, outlets report.

It wasn't until November 2020, when she was arrested a third time, that she was remanded in custody.

'I'm Evil, I Did This'

During her months-long trial, prosecutors told jurors of damning Post-It notes allegedly written by Letby and found in her home.

"I'm evil, I did this," read one. "I killed them on purpose because I'm not good enough to care for them," read another.

Paperwork relating to her alleged victims was also recovered from her residence, per The Guardian.

Earlier in the trial, Dr. Dewi Evans testified that one of the victims, referred to as Child G, suffered from irreversible brain damage, allegedly at the hands of Letby, after the infant was said to be force-fed massive amounts of milk, PEOPLE previously reported.

In another instance, according to the BBC, Letby allegedly and fatally injected two newborn triplets with air, causing their veins to turn "bright, bright blue" and their stomachs to resemble that of movie character "E.T.," the babies' father testified.

Both babies died within 24 hours of each other.

Letby's trial continues.