A psychiatric patient who had killed her mother attacked two women with a butcher's knife as they were going to work, an Old Bailey jury has heard.
Kerry Clark, then 22, managed to fight Nicola Edgington off but Sally Hodkin, 58, died when her neck was cut.
Ms Edgington, 32 from Greenwich, south-east London, admits carrying out the attacks in Bexleyheath in 2011, but denies murder and attempted murder.
The court heard she killed her mother in 2005 in Forest Row, East Sussex.
Ms Edgington's plea of manslaughter due to diminished responsibility was accepted by the prosecution on that occasion.
Before the attack in Bexleyheath, Ms Edgington went to Queen Elizabeth Hospital in Woolwich, but walked out before she could be admitted as a voluntary inpatient, jurors were told.
Her condition had deteriorated after she stopped taking her medication, the court heard.
After leaving the hospital she got the bus to Bexleyheath where she bought the knife and attacked the two women.
Mark Heywood QC, prosecuting, said: "She approached and deliberately and viciously attacked each of them without warning, without any provocation.
"She used the weapon forcefully and purposefully in each attack. She was controlled and she was rational."
'Intention to kill'
He said Mrs Hodkin was "overwhelmed" and "she died almost immediately from the catastrophic injuries inflicted on her".
The prosecution said Ms Edgington claimed her responsibility was diminished because of her mental state.
However it rejected this claim, saying she acted deliberately and "intended to kill".
The court heard she was treated as an inpatient by the Oxleas Trust and was treated for schizophrenia with emotionally unstable personality traits.
The prosecution says she has a borderline personality disorder and her mental state is variable.
The trial continues.