The Government denied that it was failing to protect the public from dangerous mentally ill people as a report said that one person a week dies at the hands of a psychiatric patient.
The report, due to be published today, says that a third of the killings were carried out by people judged not to be a danger. One in six were blamed on the failure to ensure patients took their medication properly.
It is also expected to reveal that 249 people were killed by patients released over the past five years.
Rosie Winterton, the Health minister, acknowledged yesterday that the Government could not force discharged patients to take medication, but insisted that the battle over public protection was not being lost.
Speaking on BBC Radio 4's The World at One, she said: "If they are discharged, there are some patients who don't continue to take medication, who don't continue to stay in touch with mental health services. At the moment we have no power to be able to say we want people to comply with treatment."
The report, Avoidable Deaths, was commissioned by the National Patient Safety Agency and produced by Professor Louis Appleby, the Government's national clinical director for mental health. Reports in The Observer and The Sunday Times claim that he will conclude that health staff were failing to identify those patients most likely to kill someone.
He is quoted as saying: "This is really to do with how mental health staff rate a person as low or high risk. Sometimes they just become desensitised."
His findings follow an inquiry into the killing of the retired banker, Denis Finnegan, 50, by a paranoid schizophrenic, John Barrett, which found doctors caring for Barrett were so intent on meeting his wishes that they played down the risk to the public.
But Ms Winterton said that 700 community mental health teams had been introduced to work with patients since 2001.
"It is important to see it in the wider context as well, of improvements and new investment in mental health services," she said. "What we need to do now is to make sure that the care that we can provide in the community is reflected in modern legislation."
The report will also reveal that 25 mentally ill patients commit suicide every week, with some 1,300 taking their lives every year. It will highlight how they do not receive enhanced support on leaving hospital.
Marjorie Wallace, the chief executive of the mental health charity, Sane, said she believed that one in three of the killings - as well as many of the suicides - could be prevented.
"It is not a question just of resources or laws, but, as has been highlighted, the failure to identify people at risk when all the red alerts were, in hindsight, flashing," she said. "It seems that those making decisions about whether a patient would discharge himself from hospital, or be allowed to leave, are so concerned to protect his civil liberties and short-term wishes that they are turning a collective blind eye to the risks a person may pose to themselves or occasionally others.
"Considering that nearly a third of those in this report who went on to commit homicide had seen a mental health worker in the previous week, it is extraordinary they were assessed as at no or low risk."