Sinn Féin President Gerry Adams will not face prosecution for allegedly withholding information relating to the rape and sexual abuse of his niece Áine by his brother Liam.
While a report by the North's Attorney General found there was "sufficient information" Mr Adams was aware of the nature of the allegations to merit further investigation of that issue, it also found that the public interest was better served by using Mr Adams as a witness in the subsequent trial.
Attorney General John Larkin QC said: "It should be open to the PPS (Public Prosecution Service) to make a public interest decision that such persons should be treated as witnesses and not treated as suspects by the PSNI or prosecuted without first having to take all those steps necessary in order to ascertain whether the evidential test is or is not satisfied."
Meanwhile, the report says: "The PPS did not follow the normal procedures which usually apply in a case in which the need to give consideration to prosecuting an additional suspect arises in the context of an existing file."
"There was certainly some evidence on the police file that indicated knowledge on the part of Gerry Adams that the abuse perpetrated against his niece amounted to rape or unlawful carnal knowledge and no action was taken to clarify the issue," the report says.
Prosecutors decided that the necessary evidential test had not been met before also deciding that it was not in the public interest to prosecute Mr Adams.
They opted to call him as a witness in the subsequent trial of Liam Adams.
Liam Adams was convicted in 2013 for the abuse and rape of his daughter, Áine Dahlstrom, in the 1970s.
Gerry Adams confronted his brother in 2000 but did not report his knowledge to police until 2009.
After Liam Adams was convicted, the North's Attorney General, Mr Larkin, was tasked with investigating the decision-making process deployed by the prosecution service.
It is stated in the report that Ms Dahlstrom does not want to pursue the matter further.
"Accordingly, we have concluded that there is insufficient evidence to meet the test for prosecution in this case," added Deputy Director of Public Prosecutions Pamela Atchison.
The report states that the PPS should have sought further clarity surrounding Mr Adams's knowledge of the abuse by his brother. It refers to an interview given to police by Ms Dahlstrom in 2006. The report states that it was clear that Áine had told Gerry Adams "what her father had done to her".
It added: "Furthermore she told police specifically that her mother and Gerry Adams were present when she accused Liam Adams of 'putting his thing in me'."
Mr Adams said he welcomed the findings and insisted that he committed no offence.
"This report underlines the trauma that allegations of abuse engender within families; the importance of every possible help and support being provided for victims and families; and the legal difficulties that surround such cases, particularly in respect of creating an atmosphere in which witnesses will come forward," he said.
"I have consistently maintained that my sole interest was in helping and supporting Áine and that in these endeavours I did nothing wrong."