An inquiry into alleged abuse at Muckamore Abbey hospital in Co Antrim has so far heard evidence from 42 witnesses but is behind schedule.
The inquiry, which started hearings in June, was set up after it was alleged that staff working at the regional hospital for adults with severe learning disabilities had carried out physical and mental abuse as well as "wilful neglect" of vulnerable patients.
The police investigation into Muckamore is the biggest criminal safeguarding probe of its kind in Northern Ireland.
Dozens of people have been told that they are to be prosecuted in connection with the probe. .
Providing an update before the Christmas break, inquiry chair Tom Kark QC said it had been an "important and productive year for the inquiry".
He said that so far, evidence had been heard from 42 witnesses.
"Some of those witnesses have had their statements simply read to us, but the great majority have come to give evidence before the panel in the inquiry hearing room (or in a couple of cases, by video link)," she said.
"It is important that I should again express the panel’s gratitude to those witnesses. I wish to acknowledge the fortitude that they have demonstrated in providing statements to the inquiry...
"Their contribution to the work of the Inquiry cannot be overstated".
Mr Kark said that while the inquiry had hoped to complete the hearing of the first phase of evidence, relating to the patient experience, in this calendar year, it had not been possible.
He said this was due to difficulties around obtaining statements "from individuals affiliated to Action for Muckamore and the Society of Parents and Friends of Muckamore, who have been designated as core participants in the inquiry".
"Since then I have met directly with leading members of Action for Muckamore at their request to explain my approach and to try to resolve any concerns they may have," he said.
"I have done what I can to deal with their concerns and have allowed for significant changes to the inquiry’s statement taking procedure to try to accommodate them.
"The inquiry must however move forward, even though some of the patient experience evidence remains outstanding and we have altered the order of evidence to ensure progress".
Mr Kark said the next hearing sessions would take place in March, April and possibly May.
He said these modules would look at issues including the budget provided for learning disability and mental health services, policy and procedures, and previous significant reports on Muckamore.
"The primary objective of this phase of the evidence will be to ensure that the Panel is fully informed of matters...," he said.
"I very much hope that by the end of this next period of evidence we will be able to hear the remaining evidence relating to the patient experience".
