A 13-year-old girl who was stabbed to death in broad daylight in a Doncaster park on Valentine's Day died at the hands of a former psychiatric patient, a court has heard.
Hannah Bonser, 26, is on trial for the murder of Casey Kearney, who was killed as she walked through Elmfield Park, close to the town centre, to meet a friend for a sleepover.
A jury at Sheffield Crown Court was told that Bonser had bought two kitchen knives that morning, having earlier told a friend she was going to stab her ex-boyfriend to death and "get anyone else who crossed her".
Bonser had spent a short time in a psychiatric hospital last year and was in regular contact with outreach workers from Rethink, a mental health charity.
The court heard Casey was walking through the park in the opposite direction to Bonser shortly after 1pm when she was stabbed once in the stomach with a six inch knife.
"The attack was sudden and caught Casey completely unawares," said prosecuting barrister Graham Reeds QC.
"There was no argument, no shouting, there was no warning of what was about to happen."
Casey collapsed but managed to dial 999 on her mobile phone and tell the operator that she had been stabbed.
She died that night, despite the efforts of police officers and paramedics at the scene and medics at Doncaster Royal Infirmary.
Bonser is said to have walked on after the stabbing, arriving at the town centre offices of Rethink 25 minutes later, where she handed over two knives and told a mental health worker she had killed a girl.
According to the prosecution, Bonser later claimed to hear voices "telling her to do things and not to do things".
The jury has been told it will have to decide whether Bonser is guilty of murder, which she denies, or manslaughter due to diminished responsibility.
The trial continues.