Alleged child abuse victim Mairia Cahill was "failed" by a disjointed Police Service of Northern Ireland (PSNI) investigation, a watchdog said.
In 2010 Ms Cahill, a grand-niece of prominent Belfast republican Joe Cahill, told officers she had been sexually abused by alleged IRA member Martin Morris - who was acquitted of rape and denies all wrongdoing - from 1997 to 1998.
In subsequent years she said she was subjected to an IRA interrogation over her allegations.
Police ombudsman Dr Michael Maguire said four officers should be disciplined over shortcomings in the police response.
Ms Cahill (pictured) said: "I am appalled at some of the information contained within the disclosure letter and I accept and commend the Ombudsman's officer."
Dr Maguire criticised the force's decision not to hold a serious case review and the circumstances of the choice to split its investigation across two units: one with expertise in terrorist cases and another specialised in dealing with victims of sexual assault.
He added: "I accept that police wanted to move quickly on the sexual allegations and to use their different expertise to maximum effect.
"While I do not agree that this led to evidence being diluted, it did bring about a disjointed approach by police in their investigations and their treatment of Ms Cahill.
"There is no evidence they considered any other approach, such as creating a team with the range of skills to investigate these matters as one case."
Ms Cahill, then aged 16, had told police she was subjected to a 12-month ordeal of sexual abuse.
She alleged republican paramilitaries conducted their own inquiry and subjected her to interrogation before forcing her to confront her alleged attacker.
Her allegations, highlighted in a BBC documentary, shone a light on how the IRA dealt with alleged sex abusers during a time when co-operation with the police in republican communities was extremely limited.
Ms Cahill said she was seeking an urgent meeting with PSNI chief constable George Hamilton about why the force did not have a serious case review and seeking assurances this will never happen again to anyone else.
She added: "Sinn Fein has as many questions to answer as the chief constable."
"They allowed people to call me a liar."
The attempted prosecutions of Mr Morris for alleged sex abuse and IRA membership - and four others accused of IRA membership linked to Ms Cahill's claims of a republican cover-up - never got to trial because three women withdrew their evidence.
A review by the former DPP in England and Wales, Sir Keir Starmer, said the Northern Ireland Public Prosecution Service's (PPS) handling of what were planned to be three separate trials had "let down" the three women.
The Ombudsman's office said: "Overall, the Police Ombudsman found that the PSNI investigation had failed the victims, but he did not support the allegations that it chose not to arrest some of the individuals concerned because they were police informants and that it had been subject to political interference."
Those failings included the PSNI's "inconsistent" approach in its investigation of some of the people suspected of IRA membership, which in one case led to an individual not being arrested and questioned.
The Ombudsman found no evidence that anyone had been protected from prosecution or that the PSNI investigation became subject to adverse political interference.
His investigation did not find that Ms Cahill had to direct how the investigation progressed, but said the force's lack of a strategy for researching information already in the public domain contributed to her mounting concerns.
Three of the officers recommended for action have been disciplined. The fourth had retired. Dr Maguire also made recommendations for changes to PSNI policies.
PSNI chief constable George Hamilton said: "At the heart of this report are three victims abused as children, who were then failed by their police service.
"I apologise unequivocally for the hurt and distress caused to them and for the failures in the police investigation.
"The Police Service of Northern Ireland fully supports the Office of the Police Ombudsman. It is an essential part of the mechanisms by which we can be held to account.
"The report found failures by the RUC in 2000, to share vital information which linked a man to the alleged abuse of children.
"Whilst PONI has stated that they are satisfied that current police practices would not allow such information to go un-investigated today, the report noted other failures in the PSNI's investigations.
"These standards fall very short of the high expectations that I and my officers set ourselves and that the public expect.
"I accept the report and we have since implemented all the recommendations made by PONI for changes to PSNI policies.
"There is now a better understanding of the importance and the need to work collaboratively across departments within the organisation.
"I can also assure the community that there have also been many changes to the PSNI since this initial report was made.
"One of these changes is the introduction of a dedicated Public Protection Branch in 2015, with specially trained officers with overall responsibility for protecting and safeguarding the most vulnerable members in our community and this demonstrates our commitment to building a safe, confident and peaceful Northern Ireland."
Copyright (c) Press Association Ltd. 2018, All Rights Reserved. Picture (c) Brian Lawless / PA Wire.