Police investigating Lucy Letby were able to uncover important evidence because they found a 'code' in her diary, officers have revealed.
Letby is the UK's most prolific child serial killer after being found guilty of murdering seven babies and attempting to murder six more, while she could face yet more charges.
When Letby was arrested and officers searched her home they found a chilling series of notes and diaries which helped them bring her to justice.
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After arresting her a second time officers found that Letby had continued to write notes which gave them further guidance on what had happened in the case.
Cheshire Police have taken to YouTube to show their own documentary about their investigation into the serial killer, and have said that Letby had a 'coded system' which once officers cracked found very useful in uncovering evidence against her.
Rob Woods, a detective inspector for Cheshire Constabulary, explained in the documentary that finding Letby's diary and the code she used helped them identify significant dates.
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He said: "The amount of material we found at her home address was, I think, a massive surprise to us when she was first arrested.
"It gave us a really good steer for the second occasion as to what sort of things we were looking for because we didn't have the complete chronology.
"So as an example, something that’s been very useful to the enquiry has been Miss Letby’s diaries.
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"They appeared to be and it became clear later that it was almost a code of coloured asterisks and various other things put in a diary that marked significant events."
Many of the notes and documents found at Letby's home were used in her trial to give the jury information as to her state of mind during the time of the murders.
Among her writings were notes saying 'I am evil I did this' and 'I killed them on purpose because I'm not good enough to care for them'.
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A psychiatrist looking through Letby's notes says they give some insight into her 'depraved thoughts and intentions' and will be the closest we ever come to understanding why she did what she did.
Letby received a whole life order for her crimes meaning she will have no chance of ever being released from prison and will die behind bars.
She faces spending the rest of her life in prison where she will be treated as a very dangerous prisoner.
Meanwhile, her refusal to attend her sentencing has led to politicians pushing for a change in the law to force criminals to be in court when their sentence is handed down.
Featured Image Credit: Cheshire Constabulary/CPS/PA Wire / Cheshire Constabulary/PA WireTopics: UK News, Crime, Lucy Letby