Four men arrested by detectives investigating allegations of historic abuse at a young offenders' centre in Co Down have been released.
The men, aged between 42 and 57, were detained as part of an ongoing probe into the former Rathgael facility in Bangor.
Three of the released men have had police files on them sent to prosecutors and the other was released pending further inquiries.
They had been quizzed about alleged incidents dating to the 1980s.
As part of the operation by a PSNI public protection unit (PPU), a fifth man was detained about alleged blackmail at another youth residential facility in Bangor - Lakewood Regional Secure Care Centre. He was also released pending a report to prosecutors.
The Lakewood facility houses vulnerable young people from across Northern Ireland.
The investigation into Rathgael and Lakewood was launched on January 13 this year.
The Rathgael site was closed in January 2007 and replaced by the Woodlands Juvenile Justice Centre.
A PSNI spokeswoman said: "Officers will be interviewing and speaking with anyone who can assist them with their inquiries to help bring those responsible to justice. Police would appeal to anyone who believes they were the victim of abuse or anyone who witnessed abuse or with any information to contact Public Protection Unit detectives."
The probe comes as a statutory public inquiry into historic institutional child abuse in Northern Ireland continues to gather evidence from suspected victims. However, it is understood the police investigation into Rathgael and Lakewood was not prompted by information passed on by the inquiry team.