The defendant claimed that in the months before the killing she was hearing voices telling her to harm other people.
Expert witness Sir Simon Baron-Cohen, a clinical psychologist, told the trial that, in his opinion, the teenager was suffering from a “highly distressing” mental disorder affecting her ability to form a rational judgment or exercise self-control.
At the start of the trial, prosecutor Samuel Skinner KC told jurors that the Crown Prosecution Service alleged the killing was murder because the girl, who was aged 13 at the time, had planned what she did after conducting online research.
Other psychiatric experts had said her actions were not caused by poor mental health.