Families of patients at Muckamore Abbey Hospital have met with the health minister to call for a public inquiry into the running of the hospital.
The County Antrim facility treats patients with severe learning difficulties and mental health problems.
It is at the centre of a major police investigation into allegations that vulnerable patients were abused by staff.
In 2019, police revealed they were looking into 1500 crimes in relation to alleged abuse at Muckamore Abbey Hospital, with hundreds of thousands of hours of CCTV footage have been reviewed by officers.
The Belfast Trust launched an investigation in 2017 following allegations of abuse of patients by staff at Muckamore Abbey and a number of employees have since been suspended.
Glynn Brown said: "We want a full public inquiry to ensure that this never happens again."
Muckamore treats people with severe learning disabilities and mental health needs.
Police are probing claims of physical and mental abuse of patients in the psychiatric intensive care unit in 2017-18.
"There have been thousands of allegations of criminal assaults perpetrated on the most vulnerable people in our society in a hospital setting.
"Only a public inquiry with full powers to compel documents and evidence will get to the truth of how management and all the organisations involved, the hospital trust, Regulation and Quality Improvement Authority and indeed police who were aware of allegations at certain times, only that type of robust investigation will get to the truth of why they have been failed and how this was allowed to happen."
Mr Brown formed the pressure group Action for Muckamore after his son was allegedly subjected to 160 assaults amid a "massive scandal".
Mr Brown claimed there had also been failings in adult safeguarding and social work.
Ms McKeegan said campaigners urged Mr Swann to make good on commitments to the patients and their families months before devolution was restored.
She added: "The numbers are absolutely terrifying.
"The families that we represent have been receiving almost daily reports from the police indicating that there are further assaults that they have established have been found on the CCTV footage.
"This is absolutely devastating to hear that your child, who in many instances is non-verbal and cannot speak for themselves, has been violated in such an inhumane way by medical staff in a hospital."