A psychiatric patient who murdered a woman six years after killing her own mother has been jailed for life.
Nicola Edgington, 32, of Greenwich, who has schizophrenia, must serve at least 37 years for nearly decapitating Sally Hodkin in Bexleyheath.
And it has emerged police officers failed to carry out checks which would have revealed she had killed before.
The police watchdog said officers had failed to carry out a check on the day of the killing in 2011.
Edgington, who was sentenced at the Old Bailey, had also been found guilty of trying to stab Kerry Clark, 22, whom she attacked shortly before Mrs Hodkin.
She received another minimum sentence of 20 years for the attempted murder, which will run concurrently.
'Manipulative and dangerous'
John Cooper, QC, mitigating, said she was a woman in crisis and had not been given the help she asked for.
But Judge Brian Barker told her: "Your actions on leaving the hospital were a consistent and calculated course of criminal conduct.
"You are manipulative and extremely dangerous.
"These were terrible acts and you must take responsibility for what you did.
"The fact you failed to kill Kerry Clark was only due to good fortune and swift reaction. What you did could not have been more selfish."
During the trial, the jury heard 999 calls made in the hours before the attacks, during which Edgington said: "I need for the police to come because I've had a nervous breakdown before and I killed someone."
In the hours before the murder, Edgington called emergency services four times asking for help, saying she was hearing voices again and that she was going to kill somebody.
She was taken to two different hospitals, although she was able to walk out.
The Independent Police Complaints Commission said:
* Police in Greenwich were not notified that Edgington was living in the area following her release from an indefinite hospital order in 2009 after she killed her mother
* Officers and police staff did not carry out a Police National Computer (PNC) check during their interactions with her on the day of the murder which would have alerted them to her conviction for manslaughter
* Officers missed an opportunity to use their powers under section 136 of the Mental Health Act when Edgington tried to leave the A&E department shortly after she arrived with police
Edgington's second 999 call from the A&E department was downgraded because she was considered to be in * a place of safety and an officer was not asked to return, despite Edgington saying she could be very dangerous
IPCC Commissioner Sarah Green said: "While our investigation found that no police officers or staff breached the code of conduct, it is of great concern that no PNC check was carried out which would have immediately alerted them to Edgington's violent history.
"Without this PNC check, both the police and staff at Queen Elizabeth Hospital, Woolwich, were without crucial information which may have influenced their future decisions, increased the urgency of the situation and could have escalated the medical attention she was given."
Ms Green said she hoped both the Met and Oxleas NHS Foundation Trust - which was managing Edgington's care after she was released into the community - would "learn lessons from this tragic case to improve the handling of high-risk individuals such as Nicola Edgington in the future."
'My world fell apart'
Mr Cooper, defending Edgington, said she had done what she was told to do; she had called police and taken herself to hospital.
He said she had also called her mental health support workers while she was on the bus she took to the scene of the killing, which was also the bus route to Bracton Centre where she had previously been treated.
He said her emergency calls showed she was "genuinely panicked".
In a statement read out to court, Mrs Hodkin's husband Paul said there was not a day since the attack that he had not cried.
He said the day he heard she had been killed was when "my world fell apart".
"The thought of not seeing her again has destroyed me," he said. "Over 40 years of marriage were brought to an end by someone who shouldn't have been on our streets."
Edgington killed her mother at her home in Forest Row, East Sussex, in 2005.
On that occasion Edgington pleaded guilty to manslaughter due to diminished responsibility, a plea accepted by the prosecution.
Then she was diagnosed with schizophrenia with emotionally unstable personality traits and was treated as an inpatient in a medium secure psychiatric facility by the Oxleas NHS Foundation Trust.
She was conditionally discharged in September 2009 and moved into a flat in Greenwich where she was being monitored by a consultant psychiatrist, a social supervisor and a community psychiatric nurse.