Police are being urged to investigate the deaths of more than 8,000 people who died while receiving mental health treatment.
The calls have been made by the Campaign to Save Mental Health Services in Norfolk and Suffolk, in a letter sent to chief constables of forces in both counties.
They say failings in mental health services may cross the threshold of corporate manslaughter - and have urged police to investigate further.
However, the Norfolk and Suffolk Foundation Trust, the NHS organisation responsible for mental health services in the region, has insisted improvements are being made.
The calls come after a mortality review found 8,440 people in the region had died unexpectedly while receiving mental health care in the past three years.
Mark Harrison, the campaign's chairman, said: "This is the biggest death crisis in the history of the NHS and it is happening in the trust charged with providing mental health services in Norfolk and Suffolk.
"The police are being asked to act because all other options to save the lives of people in mental distress have failed."
Forces in both Norfolk and Suffolk are introducing the controversial 'Right Person, Right Care' approach, which will see officers only respond to mental health-related calls if there is an immediate threat to life.
The constabularies argue this measure will free up officers to focus on investigating crime, with police spending a significant amount of time responding to welfare concerns and conveying NHS patients.
The campaign group is specifically asking police to investigate deaths in which a prevention of future deaths report has been published by coroners - of which there have been 39 in the past decade - and those with similar circumstances.
Prevention of future death reports (PFD) are published by coroners following inquests when they feel organisations must take action to prevent other people from dying in the same circumstances.
When these are sent to organisations, they are given 56 days to respond outlining what they are doing to address the coroner's concerns.
The trust, which has not received a PFD yet in 2023, said it has launched a review of the previous reports it has been sent to ensure improvements have been made.
Its new chief executive, Caroline Donovan, has also appointed a patient safety advisor to examine this area.
But the campaign group has argued people have continued to die under similar circumstances and that lessons have not been learned.
Mr Harrison added: "There has been a deafening silence from the bodies who have overside of mental health - NHS England and the Department for Health and Social Care.
"That is why we are also demanding an independent statutory public inquiry so lessons can be learned and practices changed."
The reports have highlighted a number of common themes, including patient observations not happening, chaotic record keeping, staff shortages and delays in mental health treatment.
The trust insists it is addressing the concerns the reports have highlighted.
An NSFT spokeswoman said: "We offer our sincere condolences to all families and carers of people affected.
"Every prevention of future deaths report has resulted in an action plan sent to the coroner to commit to actions that are needed to improve care.
"We can assure all families and carers that we are working hard to learn from these incidents and do our best to ensure they are minimised in future."
A Norfolk Constabulary spokeswoman confirmed the chief constable received the campaign's letter on Tuesday morning and would be "assessing its contents".
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here