The Broadcasting Authority of Ireland report into the Mission to Prey programme has found significant failures of editorial and managerial controls within RTÉ.
RTÉ is to be fined €200,000 following what the BAI said were serious breaches of the Broadcasting Act 2009.
The BAI found that the programme was not fair in that it broadcast serious, damaging and untrue allegations about Fr Kevin Reynolds.
It found that the means employed to make the programme, including secret filming and a doorstep interview, unreasonably encroached upon Fr Reynolds’ privacy.
It found RTÉ had fully co-operated with the investigation.
However, it said it was a source of regret that RTÉ did not choose to waive its claim to privilege in the solicitor/client relationship between itself and its in-house legal staff.
The BAI said that RTÉ submitted a detailed response to the inquiry, but the relevant individuals associated with the programme declined the opportunity to make submissions to the investigator.
However, programme makers Aoife Kavanagh, Brian Pairceir and Ken O'Shea, as well as Managing Director of News and Current Affairs Ed Mulhall, did attend meetings with the investigating officer.
Producer Mark Lappin, who was outside the country, did respond to written questions.
Following completion of the report, RTÉ was invited to make a further submission, in which it accepted the finding that it had breached the particular sections of the Broadcasting Act 2009.
The station also accepted that the defamation of Fr Reynolds was one of the most significant errors made in its broadcasting history and acknowledged that the material relating to Fr Reynolds should never have been broadcast.
The four programme makers also made a further submission to the authority on foot of the report's completion.
The BAI said their submissions were all different but included expressions of deep regret surrounding the circumstances that gave rise to the defamation of Fr Reynolds and the damage caused to him.
They also raised issues around procedural matters of the investigation process and the report of the investigator, with which they disagreed.
They also claimed that all matters that informed the decision-making in relation to the programme were not given appropriate weight by the investigating officer.
They also claimed that the unauthorised leaking and publication of documentation had prejudiced their rights and seriously undermined the entire process, thereby damaging them.
The BAI said it wished to stress that its finding should not be construed as a deterrent for broadcasters engaging with investigative journalism.
A solicitor for Fr Reynolds said they had expected the report to be published next week and will consider the report before commenting.
Robert Dore said Fr Reynolds will be celebrating mass in Ahascragh this weekend but appealed for the media to respect his privacy.
Aoife Kavanagh resigns from RTÉ
Ms Kavanagh announced this evening that she was resigning from RTÉ and apologised to Fr Kevin Reynolds.
However, she said that she had acted in good faith in the making of the programme.
She said: "I would like to take this opportunity to apologise to Fr Kevin Reynolds for the hurt caused to him by the Prime Time Investigates programme.
"I would also like to apologise to those who work with victims of sexual abuse if this controversy has in any way made their work more difficult.
"While acknowledging that mistakes were made I believe that I acted objectively and in good faith throughout the making of the programme.
"In this regard I do not accept many of the findings of the Investigating Officer in relation to the manner in which I carried out my work."
RTÉ accepts BAI's findings
RTÉ has described the defamation of Fr Kevin Reynolds by Prime Time Investigates as one of the gravest errors in its history.
It has said that it accepted the BAI findings.
In a statement, the broadcaster said the Director General and Chairman of the RTÉ Board have reiterated their deep regret for the errors that were made.
It said all the recommendations Ms Carragher made had been responded to by RTÉ and it is committed to embedding new structures and standards.
It pointed out that 500 staff had already been trained in new journalism guidelines and that key management positions would be filled shortly.
It said it was its aim to ensure that such a defamation never happens again.
None of the staff involved in the making of the programme remain in position.
Mr Mulhall retired some weeks ago and Mr Lappin has moved abroad.
Mr O'Shea and Mr Pairceir have been transferred within RTÉ, but are subject to a further investigation by an external board that will conclude shortly.
RTÉ also published the review of editorial processes commissioned from Professor John Horgan today.
It stresses that it has already implemented most of the recommendations.
Programme was shoddy and unprofessional - Rabbitte
Minister for Communications Pat Rabbitte has said that the report is more serious than he expected, describing the programme as shoddy, unprofessional, cavalier and damaging.
Mr Rabbitte said there was now a fundamental challenge to RTÉ to re-establish its reputation and rebuild trust.
He said it was quite disturbing that a man's character should be traduced in such a cavalier fashion.
The minister said it was beyond belief that the programme should put together a piece of work based on uncorroborated gossip.
He said RTÉ's Director General Noel Curran was unfortunate in his timing in that the programme was conceived before he took up his post.
Mr Rabbitte said a commendable raft of changes had been put in place, however he said although a lot had been done there was more to do.
He said his confidence in the board had been shaken and he has called a meeting of the board and the chairman at 8am Tuesday morning.
The minister said ultimately the board is charged with the governance of RTÉ.
Carragher finds note-taking was inadequate
In her report, BAI Investigating Officer Anna Carragher found that there were misjudgements by individuals, while other factors were more systemic.
Ms Carragher found that the standards of the production team on the ground, Ms Kavanagh and Mr Lappin, fell short of what should be expected.
She said interviews with significant sources were not documented and there was almost a complete absence of documentary evidence.
Ms Carragher expressed concern that the credibility of key sources was not sufficiently interrogated and that weight was given to the repetition of some allegations by individuals who were not personally questioned by the team.
She also found that key editorial meetings were not noted or minuted.
Ms Carragher found that note-taking was nonexistent or grossly inadequate at all stages of production and that in future a record should be make of key editorial decisions.
She also found there was a lack of scrutiny and challenge within the department and an over-reliance on the team's past experience, which led them into a "group-think" mentality, where they were convinced that the "facts" verified their assumption and led them to interpret the offer made by Fr Reynolds to take a paternity test as not genuine and a tactic to derail the programme.
Ms Carragher found that the secret filming and doorstep interviews encroached upon Fr Reynolds’ privacy.
However, she took the view that the RTÉ guidelines on the issue were ambiguous and capable of varying interpretation.
Ms Carragher found it surprising that the legal affairs department became involved very late in the process, less than two weeks before transmission.
She said it was highly undesirable that the reporter was the sole point of contact between Fr Reynolds’ solicitors and RTÉ.
Also a piece of correspondence was not forwarded to the legal department by the production team on the day of transmission.
While it was impossible to say definitively whether there might have been a different outcome if it had been, she said it may be that this would have been the case.
She said it is highly desirable that legal affairs have earlier input into programmes that are likely to be high-risk or contentious.