The Garda Siochana Ombudsman Commission (GSOC) has come under attack for not releasing information for the inquiry.
Sean Guerin found that the Ombudsman took the same approach as the force when faced with some of the corruption and malpractice allegations.
He said GSOC was similar to both the Garda and the Department of Justice in that it did not heed the voice of a whistleblower.
The barrister said the oversight body had made a striking finding in one case that the watchdog had seen through to completion but did not detail the issue.
“The papers I have seen suggest the approach adopted by GSOC was ultimately broadly similar to that of An Garda Siochana,” the Guerin report said.
“The final disciplinary recommendation, however, was consistent with the Garda approach, ie that individual members of An Garda Siochana should bear responsibility for the conduct of their own investigations, regardless of their inexperience or the apparent want of direction or guidance from supervisors or management.
“While the independent investigative function that Gsoc exercises is an important one in the public interest, it appears to be no guarantee of a different disciplinary outcome.”
The review was told that important documentary material held by the Garda ombudsman could not be made available without appropriate safeguards.
Mr Guerin said this approach came too late in the day of his eight-week deadline.
In his resignation letter on Wednesday Alan Shatter said he was surprised that the Garda Ombudsman had not passed on documentation to the Guerin inquiry.
Mr Shatter said complaints to the watchdog and how they were handled were relevant to the way he dealt with issues relating to Sgt Maurice McCabe.
PA