A RTÉ documentary, in partnership with the the Irish Mail on Sunday reporter Anne Sheridan, examines the Catholic Church's handling of allegations against the former Bishop of Galway, who died in 2017.
His niece, Patricia Donovan, claims he first raped her at the age of five and that the sexual abuse continued for years.
Mr Elliot found her account of what she experienced “entirely credible”, describing Bishop Casey as, on balance of probabilities, “an offender, a sexual predator."
"The fact of the matter is that individuals have come forward and spoken about… numerous sexual activities, some consensual, others not. Many involved very young people. That is wrong and there is no justification for that, and it should have been stopped.
"Those that have been distressed and hurt should be helped and supported by the Church. That is a major priority.”
Patricia Donovan tells the documentary of "The horror of being raped by him when I was five.
"The violence and it just carried on in that vein. He had no fear of being caught. He thought he could do what he liked, when he liked, how he liked… He was almost, like, incensed that I would dare fight against him, that I would dare try and hurt him, I would dare try and stop him... It didn’t make any difference.
“I feel so absolutely and completely and utterly betrayed by the Church I was brought up in.”
The documentary, called Bishop Casey's Buried Secrets, also reveals how the Limerick Diocese paid over €100,000 in settlement to one of Bishop Casey’s accusers after Casey’s death.
In early 2006, the Irish Bishops announced that Eamonn Casey was moving back to Ireland from England to retire. By this stage, the Vatican had now received at least two allegations of child sexual abuse against Bishop Casey.
Bishop Casey consistently denied all the allegations of child sexual abuse made against him. Although all the complaints were reported to An Garda Síochána, he was never charged with, or prosecuted for, any sexual crimes.
He was prepared to go to court to defend his reputation after two of his accusers brought civil cases against him.
If you have been affected by any of the issues raised in this article, you can call the national 24-hour Rape Crisis Helpline at 1800-77 8888, access text service and webchat options at drcc.ie/services/helpline/ or visit Rape Crisis Help.