A 28-year-old woman arrested in the police investigation of patient abuse at Muckamore Abbey, in Co Antrim has been released
Muckamore treats people with severe learning disabilities and mental health needs.
Police are investigating claims of physical and mental abuse of patients in the psychiatric intensive care unit near Antrim town in 2017-18.
They suspect there were 1,500 criminal assaults over a number of months in a ward with six beds in the hospital.
At least 40 members of staff have been suspended.
Scores of staff and managers have also resigned or retired.
The arrest on Wednesday is the seventh in the police probe. Police said she was released pending a report to the Public Prosecution Service.