Hannah Comber, a 74-year-old patient with schizophrenia, was found dead at Heatherside Hospital, near Buttevant, on June 22, 2006.
Ms Comber died as a result of asphyxiation, occurring when she slipped in her sleep after being placed in a chair with a restraint belt.
A HSE report was carried out into the circumstances surrounding the death of Ms Comber, reportedly at a cost of up to €90,000.
In response to a request made under the Freedom of Information Act, the HSE refused to release this internal report, citing ongoing legal proceedings relating to the case.
A judgement was handed down in the High Court in January in legal proceedings taken by two individuals who were involved in the incident against the Nurses and Midwifery Board of Ireland.
The HSE refused to say whether it was aware of separate legal proceedings currently underway with a third party.
The HSE also refused to release the full report into Ms Comber’s death under the Freedom of Information Act as information gathered during the investigation was given in confidence.
In a statement, the HSE said: “Unfortunately the HSE does not expect to be in a position to publish the report in full because the investigation was carried out under a process called ‘trust in care’.
“Under that process, which has been agreed with staff representative bodies, those taking part are entitled to expect confidentiality.”
“We will shortly publish the report recommendations and its terms of reference, which is as much as is open to us to publish.”