Police, social workers and doctors should be forced to share details about potentially dangerous people, a police chiefs' organisation has said.
Lin and Megan Russell were killed by Michael Stone 10 years ago
A new report into killer Michael Stone found facts about his state of mind were not passed between agencies.
Brian Moore, from the Association of Chief Police Officers, says avoidable tragedies could continue to occur without changes to regulations.
He says too much importance can be given to patient confidentiality.
This week's report into the care and treatment of Michael Stone stopped short of saying the 1996 murders of Lin and six year-old Megan Russell in Kent could have been prevented.
But it revealed a picture of agencies not communicating with each other, of records being lost and of warnings not being acted upon.
Mr Moore, deputy chief constable of Surrey Police, said there needed to be a "clear legal framework mandating the obligation to share information".
He said: "There is no doubt that in the past there have some violent deaths and serious assaults that may have been prevented if public authorities such as the police, social services and health had shared information about the risk posed by individuals who have come to their attention or been in their care.
"However, despite numerous public inquiries and recommendations, there is still incoherence and ineffectiveness in the way agencies share information about risk."
Some professional cultures placing the duty to maintain confidentiality higher than the duty to protect from violence, Mr Moore added.
"The overall picture is one of uncertainty, lack of clarity and, a lower standard of risk assessment than the public have the right to expect," he said.
"Many protocols, advice and guidance have been developed over the years, and although well-intentioned, they lack effectiveness and accountability. "
A joint Acpo and Home Office Working Group is currently looking at a structure for agencies to share appropriate information about people who represent a risk.
Mental health charity Sane backed Acpo's call and said its own research had found confidentiality was often cited as the reason for a failure to take action.
"Confidentiality can be a barrier not only to protection of the public but to the long-term protection and safety of the mentally ill person himself," said Sane chief executive Marjorie Wallace.
Sane looked at 69 inquiries into killings by people in contact with mental health services and found there had been a breakdown in communication between agencies in 90% of cases.