Scribbled notes by the neonatal nurse Lucy Letby, used to help convict her of murdering seven babies, were written on the advice of professionals as a way of dealing with extreme stress, the Guardian has learned.

The notes were relied on as amounting to a confession by the prosecution during her first trial and in the court of appeal, but sources close to the case said they were produced after counselling sessions as part of a therapeutic process in which she was advised to write down her troubling thoughts and feelings.

Densely written on Post-it notes and a torn sheet of paper, they were overwritten in places and sometimes highlighted in capitals. They included the words: “I am evil I did this,” “I killed them on purpose because I am not good enough to care for them and I am a horrible evil person,” and “hate.”

The prosecution used the notes to help build the case against Letby, ending the opening speech highlighting the phrase: “I am evil I did this.” Throughout the trial the jury was repeatedly reminded of that statement, and encouraged to interpret the notes literally.

But in the same notes Letby also said: “Not good enough”, “Why me?”, “I haven’t done anything wrong”, “Police investigation slander discrimination victimisation”.

Now widely referred to in the media as the confession notes, they were written after some of her colleagues started suspecting her and also referenced her family and pets, colleagues at work, and described repeated suicidal thoughts: “Kill myself right now”, “help”, “despair panic fear lost”, “I feel very alone and scared”.

There have been mounting questions in recent weeks over the safety of Letby’s conviction, against the backdrop of a public inquiry that is set to begin receiving evidence next week. A group of leading experts have called on the government to postpone or change the terms of reference of the inquiry over these concerns, including questions about some of the evidence presented at the trial.

Sources close to the case have told the Guardian that the Countess of Chester hospital’s own head of occupational health and wellbeing, Kathryn de Beger, encouraged Letby to write down her feelings as a way of coping with extreme stress. Letby’s Chester GP also advised her to write down thoughts she was struggling to process, according to these sources.

David Wilson, a professor of criminology at Birmingham City University, who specialises in serial killers, said in his view the so-called confession notes were “meaningless” and had no value as evidence, particularly if they had been written as part of counselling. “Many people will say things when they are under stress and feeling bereft, that seem to imply one thing but mean nothing at all, other than reflecting the underlying stress.”

“I always thought Letby’s notes were meaningless as evidence. If they were written as part of therapy you can underline that point three times and write it in bold and capital letters,” he added.

Letby was convicted last August of murdering seven babies and attempting to murder six others. In a retrial that ended in July she was convicted of attempting to murder a seventh. The notes did not feature in Letby’s appeal application, which was rejected.

The prosecution’s presentation of the notes was a key “gotcha moment”, according to Wilson. From his experience of trials, such moments tended to set the narrative for the whole proceedings. He believed they could have been very influential on the jury, especially when other evidence was technical and hard to understand, he said. Such moments “catch the jury’s attention and once you’ve caught it, it is really hard in our adversarial legal system to present alternatives successfully”, he added.

The notes were written at some point between July 2016, after she had been taken off the ward, and her arrest in July 2018. During this period she had been removed from her nursing duties after a cluster of deaths. She was told not to talk to most of her colleagues and so felt isolated and distressed, according to sources.

Nursing sources have said Letby was aware that senior consultants were talking openly about there being a serial killer on the unit and that gossip was pointing at her as someone who was on shift for many of the deaths.

Journalling, or writing down disturbing thoughts, is encouraged in general psychotherapy, according to Richard Curen, the chair of the Forensic Psychotherapy Society, who has worked as an expert witness and with victims and offenders for 25 years. “Doodling, journalling is a way of taking control of your thoughts. I don’t think it relates to a confession of any kind,” he said.

He added that Letby’s response on the notes in court was “robust, and seems right – she wrote down how she was being made to feel”.

“It’s useful to put words on paper to short-circuit overthinking when there’s a whirlpool of really confusing and disturbing thoughts going round and round in your head,” he said. “Once they are externalised you can maybe put them to one side and carry on with what needs your attention.”

De Beger gave Letby counselling over several sessions as part of support arranged by the hospital. Letby’s notes refer repeatedly to De Beger and to Bergerac, which appears to derive from the sound of her name.

The notes also mention her cats, Tigger and Smudge, her dog, Whiskey, and Tiny Boy, thought initially by investigators to be a reference to babies she killed but in fact her nickname for the small Yorkshire cross terrier dog, according to the sources close to the case.

Asked about the notes during her trial, Letby said she had always written things down to help understand her feelings, and that they were random thoughts. She said she was questioning herself and whether she had unintentionally done harm by not knowing enough or not being a good enough nurse, because of what was being said about her by doctors.

She denied in her first trial that the notes meant she killed or harmed babies. She said De Beger was “someone she was seeing” for support. The fact that writing the notes had been advised as part of counselling was not mentioned in court.

The defence argued during the trial that the notes represented Letby’s anguished state of mind when she was accused of killing babies and not “guilt”. “Anguish not guilt. A young woman who trained hard to be a nurse … who loved what she did, and found she was being blamed for the deaths of the babies she cared for,” the defence counsel Ben Myers told the jury. But no expert forensic psychologists were called to give evidence on how to interpret the notes.

The Countess of Chester hospital said it could not comment while the inquiry and further investigations were ongoing.