Experts say "at risk" patients like triple murderer Anthony Hardy are less likely to slip through the net after assessment guidelines were tightened.
Hardy was not deemed mentally ill when he killed the women
Hardy was allowed out of a psychiatric hospital despite a unseen doctor's report that he posed a risk to women.
Mental health charity SANE said the report should have been a "red alert" to agencies monitoring such patients.
However, changes to mental health laws since the 2002 killings has improved information sharing, say the experts.
"Key reports, such as that by the forensic psychiatrist who warned that Hardy posed a high risk of violence, should act as a red alert and be available to any discharging panel," said Marjorie Wallace, chief executive of SANE.
"Patients with a history of potential violence should not be discharged with only limited information given to those responsible for monitoring them in the community."
She said those monitoring patients released into the community should have the full facts.
Since Hardy carried out the killings, mental health experts say guidelines under the Mental Health Act have been tightened to improve information sharing.
Patients' details are now passed on to the Multi-Agency Protection Panel (MAPP), which monitors them to protect the public - something not previously done because of patient confidentiality.
"There have been improvements in the sharing of information," said Gerard Bailes, a forensic clinical psychologist for the Forensic Psychiatric Service in East Anglia.
Elizabeth Valad was killed shortly after he was released
"But risk assessment is a risky business. The grey of human behaviour doesn't always fit with the black and white of a legal document."
Hardy, from Camden, north London, was jailed in 2003 for the killings of Sally White, Elizabeth Valad and Bridgette MacClennan.
He had spent months in a psychiatric unit for after being detained under the Mental Health Act for daubing abuse on a neighbour's door.
But he was released in November 2002 by a hospital panel, which had not seen a report warning he was a risk to women.
The year-long inquiry found Hardy's mental state was clinically normal, not manic, depressed nor psychotic, when he killed the women.
But on hearing the report Tina Harvey, who says she was attacked by him in December 2002, said: "Sorry, I've just got to laugh.
She added: "He was trying to crush me and kill me. He was not the character of the personality disorder. It was of a mentally ill man."