A carer has been filmed dancing naked around a severely disabled young man at a residential care home in Margate.
The video was filmed during an alcohol-fuelled party at Thanet Lodge boarding house, part of the trust that included the now closed Royal School for Deaf Children.
The mother of the blind and deaf man said she "couldn't believe" people she trusted could behave that way.
Kent Police found no crime had taken place. The female carer was sacked.
A total of four people lost their jobs in September 2014 when a whistleblower handed in the video.
They included team leader Yvette Surrage and support workers Jane Smith and David Gardiner who were all seen in the footage.
Senior support worker Ben Healy, who filmed the incident and was heard encouraging his colleagues, was also dismissed.
Ms Surrage was seen dancing semi-clothed and Ms Smith was seen dancing naked around the young man. It is not clear whether Mr Gardiner was in the room when Ms Smith did this.
The mobile-phone footage, given exclusively to BBC South East, shows carers also used sexually-explicit language.
The young man has serious learning difficulties, which meant he needed 24-hour care.
His mother, whose identity has not been revealed, said he probably left his bedroom to look for help and wandered into the common room where loud music would have drowned out any attempts to get assistance.
"He did used to do a lot of self-harming where he could bash the side of his face, bite his hands, thump the floor - we never knew why.
"The fact that his behaviour has changed so drastically for the better since he's moved, leads me to believe that this went on and maybe worse, who knows, for a long time, " she said.
The mother believes more should have been done to protect her son and legal action taken against those caring for him.
Kent Police saw the video but decided there was not enough evidence to investigate further.
In a statement, the force said: "Whilst the acts seen in the video are wholly inappropriate and irresponsible, they do not fit the criteria for a specific criminal offence."
Dr Noelle Blackman, chief executive of the charity Respond, described the footage as "humiliating" and "absolutely horrible".
She said: "Their [the carers] duty is to be there to provide support to this man - this is not providing support this is having their own debauched party - that's neglect if nothing else.
"And to me it's abusive. I think they're humiliating him."
When BBC South East contacted the carers, Ms Surrage said there was no abuse and no poor practice. She said no conviction or prosecution took place because there were no young adults involved.
David Gardiner said he felt the incident brought no harm to the students but admitted he should not have allowed it to go on. He said he cared for the young adults to the best of his ability.
Jane Smith said she was at a difficult point in her life and deeply regretted what happened.
Ben Healy said there was no footage that displayed him acting inappropriately.
The Royal School for Deaf Children and its post-16 department Westgate College closed in December after the John Townsend Trust went into administration.
The Care Quality Commission (CQC) revealed on Tuesday there had been "institutionalised failings and abuse" at the residential accommodation attached to Westgate College, which it ordered the trust to close down last November.