An arrest has been made in connection with abuse allegations at Muckamore Abbey Hospital in County Antrim.
A 30-year-old man was arrested by officers in Antrim on Monday morning.
In recent months police have been investigating thousands of incidents after allegations were made about the physical and mental abuse of patients.
The hospital provides treatment for people with severe learning disabilities and mental health needs.
It has been alleged a number of vulnerable men and women were abused.
Twenty-eight staff, mainly nurses, have been suspended at the hospital since 2017 when allegations of ill treatment first began to surface.
In August 2018, it was reported there had been 53 assaults on patients by staff at the hospital – five of those incidents were investigated and substantiated.
Formal action was taken by the Regulation and Quality Improvement Authority (RQIA) in August 2019, when the health regulator issued three enforcement notices about staffing and nurse provision; adult safeguarding and patient finances.