The "cannibal killer" case of Peter Bryan - a mental health patient who police found eating one of his victims - shows the mental health system is struggling, campaigners say.
Peter Bryan's conviction has prompted calls for an inquiry
Bryan, 34, was arrested after he killed Brian Cherry, 43, at the victim's London flat.
He went on to kill Richard Loudwell, 59, at Broadmoor special hospital in April last year, while on remand.
He was sentenced to life after pleading guilty to two manslaughters on
the grounds of diminished responsibility.
At the court case, it emerged that he was a convicted killer who had been sent to Rampton secure hospital in 1994 for beating a shop assistant to death with a hammer, but was freed in 2001 after applying to a health review tribunal.
Michael Howlett, the director of mental health charity the Zito Trust, has called for an inquiry into how Bryan was able to leave a mental health unit to carry out his first killing.
Mr Howlett said the case showed that mental health services were struggling to cope with dangerous patients.
He said: "We're very concerned. It's an appalling case, and is another example of somebody who has been into a high security hospital, been discharged with conditions and has gone on to kill.
"The conditions are breached and nothing happens, when what should happen is that they are returned to hospital immediately."
Mr Howlett said the court had heard Bryan had been skilled at hiding his symptoms, but that this was not an excuse for allowing him to discharge himself.
"Given his background, and the fact that he had already killed, the specialists should have been on the lookout for signs which were masking his real symptoms," he said.
"Over the last 10 or 15 years mental health services have consistently failed to prevent homicides and serious attacks by people who are already known to have a history of violence.
"These cases raise real concerns about whether our mental health services can cope with the severity of the situations they're now being asked to deal with."
Mr Howlett called for the community-based care system to be examined.
"We do not want a return to institutional care but there are people in the community who should not be there," he said.
"Cases like this show that the mental health services simply can't cope."
The mental health charity Sane voiced similar concerns, saying the case showed psychiatric services were having to take "unacceptable risks" with people's lives.
Its chief executive, Marjorie Wallace said: "We are becoming increasingly concerned about the numbers of people with a mental illness or disorder who are discharged from hospital by a tribunal, or simply allowed to walk off wards into the community without the police or community teams being alerted or adequate arrangements being made for supervision.
The psychiatric services seem to be working under such pressures that they are being forced to take unacceptable risks /CPS:QUOTE>
Marjorie Wallace Sane
"It is well known that it is within the first few days after leaving hospital that people are most at risk of harming themselves or, occasionally, others."
She said the charity's analysis of similar cases revealed the same "cocktail of risks" which have not been adequately assessed or acted on.
"The psychiatric services seem to be working under such pressures that they are being forced to take unacceptable risks with the lives of both patients and occasionally the public," she said.
In a statement, Sheila Foley, chief executive of the East London and the City Mental Health Trust said there would be an independent inquiry following the "unusual case".
She added: "But I would like to give my personal assurance that the Trust is doing and will continue to do everything in its power to improve the services we provide to local people."
Last month Health Secretary John Reid ordered an inquiry into the killing of a cyclist by a paranoid schizophrenic a day after he walked out of a mental hospital.
At the time, the health secretary said the stabbing of Denis Finnegan in September 2004 by John Barrett, 42, in Richmond Park, south-west London, raised questions.
He said there were implications at both local and national levels.