Campaigners plan to use the legal system to pressure the government to make a decision regarding the investigation into mental health deaths.
The chair of the inquiry asked the health secretary for additional authority to compel witnesses to testify in March.
Families of the deceased have requested a judicial review to determine whether the prolonged wait for a response is legal.
The next steps in the investigation are being thought of, according to the Department of Health and Social Care.
The Essex Mental Health Inquiry was established in 2021 to look into the deaths of individuals under the county's mental health services over the preceding 20 years.
Dr. Geraldine Strathdee, the chair, has expressed her frustration at the lack of witnesses, particularly former and present employees at the NHS trusts in question.
She recently released a second letter to Health Secretary Steve Barclay in which she pleaded for statutory authority for her investigation and expressed new safety worries.
Over a 21-year period, the Essex Partnership University Trust (EPUT) and its predecessor organizations, according to the inquiry, were responsible for about 2,000 deaths of patients.
The trust's current chief executive, Paul Scott, has disputed this number.
In a letter obtained by the BBC, attorneys representing some of the families of the deceased stated that Dr. Strathdee's lack of response was an "intolerable situation.".
They claimed that they made the decision to request a judicial review because they "were not prepared to wait any longer.".
Melanie Leahy, whose son Matthew passed away in 2012 at the Linden Centre in Chelmsford while he was an inpatient, claimed that she and other families were "hurt and frustrated by the government's lack of action and Mr Barclay's silence.".
Patients are still dying, and we've been waiting for a conversion of the current toothless inquiry for months, she said.
"We just don't understand why it is taking so long to announce the next step in getting the much-needed statutory public inquiry into Essex mental health services underway," the group said. ".
Every death in a mental health facility is a tragedy, according to a spokesperson for the Department of Health and Social Care. The inquiry was started to look at inpatient mental health deaths in Essex between 2000 and 2020 as we work to improve mental health services nationwide.
"We want to express our gratitude to everyone who took part in the investigation to help increase patient safety. However, it is disappointing that some current and former employees have not participated to the extent anticipated and that the inquiry has not been successful in accessing all of the information it has requested.
"We are carefully determining the inquiry's next steps and will provide an update as soon as possible.
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