The Royal Ulster Constabulary (RUC) had information about alleged abuse of children a decade before it was reported but did not investigate it, the Police Ombudsman for Northern Ireland said.
The watchdog found the force's Criminal Investigation Department received intelligence in 2000 which linked a man to alleged harm of children.
It came to light while the watchdog examined the Police Service of Northern Ireland's (PSNI) handling of reports made to it in 2010 by Mairia Cahill.
The Ombudsman said the RUC's Special Branch received additional intelligence in 2000 through to 2001 suggesting that a man had abused children and that the IRA was investigating this.
Dr Michael Maguire has satisfied himself that the PSNI disclosed all relevant material to prosecutors in 2014.
He added: "However, when the RUC received this intelligence it was not disseminated and there is no evidence of any police investigation or inquiries as a result of it.
"The material was sufficiently specific that had police undertaken even cursory inquiries they would have identified potential victims of abuse."
He added: "I am satisfied that current police practices would not allow such information to go un-investigated today."
Alleged abuse victim Ms Cahill said she was appalled at some of the Ombudsman's revelations.
"Someone needs to provide me with an explanation as to why intelligence was received by the RUC...and it sat from 2000 to 2010."
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