The family of Jenny Morrison, 51, immediately condemned the system that allowed Anthony Joseph to kill his "compassionate and highly respected" social worker in a care in the community hostel.
Joseph, 27, expressed no emotion as the jury of five women and six men decided by majority that he was guilty of manslaughter due to diminished responsibility. They rejected the defence's claim that he had been too insane to understand the illegality of his actions.
His Honour Judge Michael Hyam, the Recorder of London, said Joseph should be sent back to Broadmoor secure psychiatric hospital indefinitely. "There is risk of your committing further offences if set at large and it is necessary for the protection of the public from serious harm to make a restriction order not subject to limited time," he said.
Wandsworth Social Services said there would be a public inquiry. But Ms Morrison's daughter, Tanya, 30, told The Independent she was angry that Joseph's condition had been allowed to worsen to the point where he killed her mother. "Why was he allowed to deteriorate over six months and how could he stop taking his medication for four months?"
Her views were echoed by mental health campaigners, after the Old Bailey trial had heard that no risk assessment had been carried out on Joseph when he was released into the community from the hospital. Furthermore he had not taken his medication for at least four months - something the social workers were powerless to enforce - and had threatened to harm Mrs Morrison.
Michael Howlett, director of the Zito Trust said: "If a patient stops taking his medication, he is not only putting his mental well-being at risk but also the safety of the public around him.
"The fact he could get kitchen knives in an environment that is not closely supervised just adds to the outrage in this horror. This is a classic case of someone being discharged improperly without a proper risk assessment.
"The situation Jenny Morrison was in was absolutely appalling."
Marjorie Wallace, SANE chief executive, pointed out that there had been 33 inquiries into such cases, with a further 30 inquiries still ongoing.
She said: "There needs to be a policy of risk assessment in general, not just for these relatively few tragic cases."
She hoped the recommendations brought in by the forthcoming review of the Mental Health Act and the new National Framework for Mental Health Services would offer improvement. "What we hope is that this is going to be one of the last cases of its kind."
Joseph had been under the care of Wandsworth Social Services, Pathfinder Mental Health Services NHS Trust and the Merton, Sutton and Wandsworth Health Trust.
An internal review recommended that risk assessment be introduced as part of a broader review. It further insisted that there should be better communication with GPs.
While acknowledging that there had been some consideration of risk when Joseph was released into the community, the report said there should be more comprehensive care plans.
The Old Bailey trial had heard that Joseph carried out the brutal killing while suffering the delusion that he was the Son of God and had been ordered to do so by his "Christ family". His parents, Roy and Maria Joseph, condemned the hostel for failing their son at the time of the death.
Wandsworth Social Services said the public inquiry into Morrison's death would be chaired by Peter Herbert, the barrister who handled the investigation into the death of WPC Nina Mackay. It added: "The inquiry team will look into the quality, scope and appropriateness of the care and treatment that Mr Joseph received from local health services.