"Sources close to the investigation have told the Mail that Girl X had been expelled from several schools, most recently for selling cannabis 'gummies' or sweets to pupils. She was caught after children became ill and teachers were informed.
'She had problems at school but she had never been in trouble with the police, she had no previous convictions and her family life seemed very ordinary,' said a source.
However, they added: 'As well as her fascination with murder and torture, Girl X told friends she was into satanism and the occult. She claimed she identified as a witch. It is baffling why she behaved this way.'
She boasted - falsely - of having killed two other people before, and talked of a desire to take bodily parts as sick souvenirs.
A parent of a child who attended the same school as her said her odd behaviour meant she had few friends.
'It was common knowledge from 2020 that she had a "kill list" of kids she wanted to kill,' he said.
'My daughter came home and told me about it, but no one took it seriously. Girl X tried to recruit other children to take part in blood rituals with her, everyone just thought she was weird and a fantasist.
'You won't find a single student that liked her.'
Giving evidence, the girl admitted she had self-harmed since the age of 12, which she said was a 'coping mechanism' for dealing with anxiety.
She then referred to her favourite film, Sweeney Todd, the famous story of a murderous cut-throat barber turned pie-maker.
She told her friend: 'It's really good and dark and gory and romantic... I'm watching for the 9000th time... you should watch it.'
Girl X also revealed an interest in serial killers such as 'Milwaukee Monster' Jeffrey Dahmer, the cannibal and necrophiliac who killed and dismembered 17 men between 1978 and 1991, 'Night Stalker' Richard Ramirez, whose 13 victims included a nine-year-old girl and a 79-year-old woman, and 'Dr Death' Harold Shipman, the English GP. suspected of killing around 250 people.
And on December 5, 2022, she sent Boy Y an advert for an underground site for people who like rape, torture and murder.
'I love watching torture vids,' she told him. 'Real ones on the dark web.'"