Four killings in Wellington last year linked to mental illness are being investigated by the coronor in a single inquest.
A Ministry of Justice spokesperson said the deaths of Cathy Stewart, Helen Silverwood, Kiaong Tan, and another man whose name is permanently suppressed, had been referred to coroner Michael Robb.
All died in the Wellington region last year and two cases involved offenders who were previously found not guilty by reason of insanity.
RNZ News understands a joint inquest will consider the capital's mental health services, but no date has been set for the hearing.
One source said joint inquiries were not a rarity, but an opportunity to look at the bigger picture.
It is also not the first time Wellington's mental health services has been the subject of coronial inquests.
In December 2012, Wellington man Zubidullah Abdullah disappeared from a locked mental health unit and killed himself.
Wellington coroner Garry Evans' response to the case was the third time he had made the same set of recommendations after the escape and death of patients from the hospital's secure mental health ward.
He found Capital and Coast DHB was aware of the risk of escape from the unit three months before Mr Abdullah's disappearance.
In another case in 2002, Mr Evans called for urgent safeguards for potentially dangerous psychiatric patients, following the brutal slaying of Hutt Valley woman Fiona Maulolo.
Ms Maulolo was killed by her schizophrenic ex-boyfriend Leslie Parr at her house in April 1997.
In his report, Mr Evans found that Parr's treatment was seriously deficient.
Mr Evans' report showed:
- Despite twice being ordered to a mental health facility over a six-month period, he was released within weeks of being transferred from Porirua to Hutt Hospital
- Capital and Coast District Health Board failed to pass on court psychiatric reports, when Parr was transferred to Hutt Hospital, which clearly identified him as a potential risk to the community
- Hutt Valley District Health Board also failed to request the missing reports
Mr Evans' recommendations included establishing a new national system to identify and manage patients like Parr and suggested placing a risk assessment sheet at the front of all files of mental health patients.
Finally, it suggested a law change allowing court forensic reports to be more freely available to those caring for dangerous patients.
Following the Raurimu shootings in 1997 - in which six people died - coroner Tim Scott criticised the lack of responsibility and co-ordination by mental health services.
Mr Scott's recommendations included:
- A consent form be signed by mental health patients allowing their files to be circulated to treatment providers on a need-to-know basis
- Treatment of mental health patients be pro-active, rather than reactive, in a bid to stop crises occurring
- The highest qualified member should be leader and shoulder ultimate responsibility for treatment and outcomes
- There be no gaps when patients are 'handed over' from one service provider to another, whether treatment is for mental or physical health
He noted that there was a two-month gap in the treatment of the killer, who was found not guilty by reason of insanity.
Mr Scott said at the time he was staggered there had been no identifiable medical professional with ultimate responsibility for the killer's care.