Severely disabled care home residents in Londonderry who could not speak suffered physical and psychological abuse, a review has found.
Some drew pictures to communicate and needed wheelchairs to move around, plus constant assistance to cope with their learning problems.
Health Minister Edwin Poots described the abuse as "disturbing".
An investigation was initiated following anonymous allegations about staff at Ralph's Close.
Mr Poots said: "This highlights the challenges we face in protecting the most vulnerable people in our society, people who cannot always speak for themselves and who rely on others for their care.
"There is no room in the health and social care family for those who exploit their position of trust by inflicting suffering and harm, or indeed standing by and ignoring others who do."
Mr Poots said no concerns remained over standards of care and there had been a transformation in the treatment over the past 18 months.
An anonymous whistleblower raised the abuse of patients in July 2012 which sparked a three-pronged probe resulting in almost a third of the total staff of 35 being suspended.
In October 2013 a police investigation found no evidence that would support a prosecution.
However, the trust's investigation discovered evidence that substantiated 22 of the original 45 allegations.
Out of the 22 were five incidents where staff physical abused patients, four incidents of verbal abuse, and 13 "other" instances of abuse, understood to be omissions in care which would include instances of neglect.
There are 16 patients with severe learning disabilities in long-term care at Ralph's Close, but the allegations directly involved 11 of them.
All 11 families have been informed of the investigation and its findings.
Nine staff members were suspended as a precautionary measure as soon as the allegations were made in 2012 with a further two placed on suspension a short time later – all on full pay.
The health watchdog, the Regulation and Quality Improvement Authority (RQIA), the third body involved in the investigation, produced a report in September 2012 when it criticised practices at the home.
These centred around "a significant number" of accidents and incidents including unexplained bruising and injuries involving residents and failure in the care plans of clients, including the administration of medicines.
RQIA found concerns relating to the protection, health and safety of residents; the use of restrictive practices; the provision of suitable staff and staff training, and the requirement of the home to notify RQIA of significant events as required under regulations.
In the intervening months RQIA carried out 12 unannounced visits, the last of which was two weeks ago when inspectors gave a glowing report in which no issues of concern were raised.
An earlier PSNI investigation found there was not enough evidence for criminal prosecutions.
Director of adult mental health at the Western Trust Trevor Miller has apologised to each of the families. He said: "The Western Trust has completed an adult safeguarding investigation on Ralph's Close.
"The findings of the investigation have been shared with the families, staff, Trust Board, the Health and Western Health and Social Care Trust, Social Care Board, the Department of Health, Social Services and Public Safety and the Regulation Quality Improvement Authority (RQIA).
"Trust staff continue to meet the families concerned and have apologised to them for any distress caused to their family members resident in the home.
"The trust would like to assure the families and the general public that it is committed to providing high-quality dignified care and continuous improvement of this service."
Mr Poots added: "The findings are disturbing, but it is always important that such issues are brought into the open so that we can take all appropriate action and secure improvements in services
"I will continue to do all within my power to stamp out abuse and create a system where there is no hiding place for those who abuse their position of trust. I cannot do this alone. It requires everyone to be vigilant and to take responsibility to protect those who are vulnerable. "