CCTV footage has revealed 1,500 crimes on one ward of Muckamore Abbey Hospital in County Antrim, the police officer leading the investigation has said.
The incidents happened in the psychiatric intensive care unit over the course of six months in 2017-18.
Police are investigating allegations about the physical and mental abuse of patients.
The hospital provides treatment for people with severe learning disabilities and mental health needs.
Twenty staff, mainly nurses, have been suspended at the hospital since 2017.
Allegations of ill treatment began to surface at Muckamore in November 2017 when it was revealed four staff members had been suspended.
In August 2018, BBC News NI reported there had been 53 assaults on patients by staff reported at the hospital – five of those incidents were investigated and substantiated.
In an interview with the Irish News, Det Ch Insp Jill Duffie described it as the “largest adult safeguarding case” of its kind undertaken by the Police service of Northern Ireland (PSNI).
Speaking to BBC Radio Ulster’s Good Morning Ulster programme, Det Ch Insp Duffie said police were examining a series of “very traumatic events” seen in more than 300,000 hours of footage.
She said officers were going through the footage “minute by minute”.
‘Repeated pattern of abuse’
She said the footage included the repeated physical abuse of patients.
“Over the period of six months we are looking at a pattern of very traumatic events,” she added.
“We have seen the repeated pattern of physical and mental abuse of the patients contained within that ward.
“These patients would not normally have been able to tell anyone what was happening to them and that is why it is so crucial in this case that we have the CCTV evidence.”
The PSNI has been in “regular contact” with the families affected.
“I do believe the families understand and they appreciate the size of the task at hand,” said Det Ch Insp Duffie.
‘Review every element’
The Democratic Unionist Party (DUP) MP Gavin Robinson repeated his call for a public inquiry into the Belfast Health Trust’s handling of the “sorry catalogue of abuse” at the hospital.
“Candour has been severely lacking,” he said.
“Every element of this horror story must be reviewed. Every system. Every decision.”
Earlier this month, Northern Ireland’s health regulator – the Regulation and Quality Improvement Authority (RQIA) – took action against the Belfast Health Trust over care standards at the facility.
Three enforcement notices have been issued about staffing and nurse provision; adult safeguarding and patient finances.
The RQIA said it had been working with the trust since February and had escalated its response to enforcement action because it felt it had no other choice.
The Belfast Health Trust acknowledged the improvement notices and said, alongside sister organisations across health and social care, it was trying to develop a model of care “which is receptive to the changing needs of patients”.