The head of Scotland Yard's murder squad has urged a review of the law to make it easier for doctors to identify mentally ill patients who could kill.
Jonathan Zito died in 1992 after being stabbed by a schizophrenic
Doctors can currently face disciplinary action for breaking a patient's confidentiality, even where they consider the person a serious danger.
Commander Andy Baker believes mental health professionals could hold the key to identifying potential killers.
But some senior psychiatrists disagree, saying such predictions are impossible.
Cdr Baker is attending a forensic science conference with leading psychiatrists and academics.
Speaking on BBC Radio 4's Today programme, he said his call was based on murder cases which he believed could have been prevented if health professionals had told police of the threat.
The threat was predominantly towards carers, parents and other loved ones, Cdr Baker said.
"There are cases where there has been a history of mental health support where someone hasn't had the confidence to raise it," he said.
"Rather than the doctor having to take the risk of sitting on it and one life being taken and one life going to prison for life, I think that doctor should be able, in confidence, to raise the issue so that it can be looked at and risk assessed."
Under the Police and Criminal Evidence Act, section 115, such threats can be raised in the interests of protecting the public.
Cdr Baker said some doctors "felt some tension between confidentiality towards their client - which I fully understand - and the issue of possibly saving a life.
"On proportionality terms, the saving of a life must come over and above that confidentiality."
However, he did emphasise that people who suffer from mental health problems were more likely to be victims of crime rather than perpetrators.
His views have received the support of mental health charity SANE.
Marjorie Wallace, the charity's chief executive, said: "Over-emphasis on confidentiality to protect patients' rights can conflict tragically with the rights of families and the community.
"Psychiatrists and mental health teams should work more closely with the police and families.
"SANE is working with the Metropolitan Police and others for an urgent change in practice and attitudes which we believe could prevent at least one-third of the 48 homicides involving mental illness each year."
Cdr Baker's call is also backed by Jayne Zito, whose husband Jonathan was stabbed to death by a mentally ill man in 1992.
Independent inquiries later found that vital information about Christopher Clunis, who was out of hospital under the care in the community programme, had not been shared.
The government is already planning enforced treatment of potentially dangerous mental health patients.