Warning - this story contains details some people may find distressing.

Muckamore Abbey Hospital was meant to be a home, a place of safety for people with severe learning disabilities and mental health needs in Northern Ireland.

But some patients were abused, allegations of mistreatment were ignored.

In 2017 the hospital became the centre of what the Police Service of Northern Ireland has called the UK's largest criminal adult safeguarding investigation.

To date police have reported 124 people who worked at Muckamore to the Public Prosecution Service. It, in turn, has directed that 58 should be prosecuted.

Central to those investigating what went on at Muckamore was hundreds of thousands of hours of CCTV footage which captured what happened on the wards over a six-month period.

The inquiry's chair said that with out it the inquiry itself may never have been established.

Staff believed the cameras were not switched on. But they were and the footage revealed 1,500 crimes on one ward alone.

One person whose job it was to trawl through the recordings told BBC News he watched vulnerable adults "kicked, trailed by their legs down corridors and thrown into a seclusion room".

"They were goaded and abused in a place where they were meant to be safe."

'Snatched comfort blankets'

This source, who asked BBC News NI to protect their identity, said the content of the CCTV footage was so harrowing they needed psychological support after viewing it.

"I cried, I kicked a bin, I felt angry and in disbelief that health workers could be so cruel to people in their care.

"The CCTV footage revealed systemic abuse where some staff nurses showed no empathy and got joy out of intentionally hurting people physically and psychologically," the source said.

The source agreed to speak to place on record the scale of the cruelty.

They also stressed that the lack of leadership and action from management over decades was reprehensible.

Staff would snatch patient's comfort blankets, dolls, or favourite book and magazines which would trigger a "kick-off".

That would lead to a "struggle" between staff and patients with the latter being restrained and staff seeing the result as something to celebrate.

Our contact said the behaviour of patients was involuntary, however the behaviour of staff was intentionally menacing.

"At times it was just neglect and then cruel neglect, one man who had been in the seclusion room and was clearly agitated banging his head off walls for over 30 minutes was made to clean up his own vomit by staff who eventually opened the seclusion door," they said.

"Another was brought to the ground and was banging his head off tiles - he was restrained - it was the intervention of another patient who came to his aid and placed a pillow under his head, it wasn't the staff but another patient," they said.

'Hauled over a nurses' station'

Few people have seen the CCTV footage.

One parent told the BBC that having seen a small part of it was enough to give them the conviction to pursue a public inquiry.

When its existence is mentioned to other families, they are visibly upset about what they have seen or heard about how it affected their child.

Our source said the pictures do not lie and have provided the police with evidence to pursue criminal investigations which are ongoing.

They told BBC News NI about several incidents that stood out, including how a male patient was hauled over a nurses' station by his shoulders. The patient's airways were blocked and he began to choke.

He was later seen being trailed down a corridor by his legs and lifted into the seclusion room where he cried and was left unattended for 40 minutes.

Others were left lying on floors with staff kicking them or just standing with their foot on their backs.

While there is no evidence of sexual abuse the source said there was "inappropriate gesturing" and "sexualising behaviour" where a member of staff would reverse inappropriately into a person's lap and lie back, but then quickly move away when another member of staff either came into a room or noticed what was happening.

They added that while not all members of staff were directly involved, there were those who stood by and turned a "blind eye".

The Belfast Health Trust's disciplinary panel screened 192 members of staff - of those 19 were dismissed or sacked.

BBC News NI understands that about 64 have been referred to the Nursing and Midwifery council, 24 referred to the Northern Ireland Social Care Council while 52 members of staff are awaiting investigation.

On Thursday, Belfast Trust said it was "truly, deeply sorry".

Its chief executive Jennifer Welsh said she took full responsibility for the "wrongs committed".

"I am truly sorry for the distress, anger, and anxiety that this Trust has caused you, and continues to cause some of you.

"The mark of a civilised society is how we treat the most vulnerable members of that society.

"I am sorry to say that your loved ones were treated by many staff in the most uncivilised way, by people who were there to care, who not only should have known better, but more importantly, should have behaved better."

Families have said they are angry the investigation of staff has been so slow with updates to families "virtually non-existent".

The person who had to watch the CCTV footage said the blame for everything that happened goes to the very top of the health trust where, over decades, people just let the hospital "drift out of sight".