The Garda watchdog has come under attack for not releasing information for the inquiry.
Sean Guerin found that the Garda Siochana Ombudsman Commission (Gsoc) 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.
Later, the Garda Ombudsman said it had gathered a good deal of documentation for the Guerin review but felt it necessary to seek assurances about its use.
It said it was regrettable the review did not see its files.
"While we were aware of the tight timescale, we were not aware of an exact fixed deadline date," the watchdog said in a statement.
Gsoc is also investigating a complaint made to its offices in relation to murderer Jerry McGrath and why he was released on bail after assaulting taxi driver Mary Lynch in 2007 a few months before he killed.
"For this reason we are reluctant to discuss the details of the cases - we must be conscious of our duty to protect the rights of both the complainant and the gardai in question. In fact, this is one of the key matters which we wished to discuss with Mr Guerin, prior to furnishing our documentation," the watchdog said.
It added: "The report is critical of some agencies and says that the same appears to be true of Gsoc.
"We would like to note in this regard that Gsoc has met and corresponded with Sergeant McCabe. However, these meetings and correspondence always took place in the context of the fact that Gsoc is expressly prohibited by the Garda Siochana Act (2005) from receiving complaints from serving Garda members."