Allegations of Garda inaction in the Omagh bombing, ministerial interference in the judicial process, and unlawful conduct by senior Garda officers are without foundation, the Minister for Justice has told the Dáil.
Mr McDowell said the Nally report into concerns about Garda activities in 1998 "concluded that there was no foundation for the allegations which it examined".
The Minister also said that no allegations were made to the report's authors that gardaí failed to pass on information in their possession to the RUC, now the PSNI, which could have prevented the Omagh bombing in 1998.
Mr McDowell also said he would not be publishing the report "for valid security reasons".
It would be "the height of irresponsibility for me to put in the public domain information that would be of use only to paramilitary terrorists in waging their campaign".
However, the report recommended the keeping of better records of North/South contacts and exchanges in intelligence matters, and the production of a written code of instructions and guidelines on intelligence-gathering and agent-handling.
It also called for consideration to be given to the desirability of legislation on intelligence-gathering and agent-handling.
The Minister said the report "is a particularly lucid and compelling document, and I believe that if people had access to it, few, if any, would dispute its conclusions".
Mr McDowell said he could not publish the report because it dealt with highly-sensitive matters involving the security of the State and the possible risk to the lives of individuals. It also described Garda operational procedures and methods, public disclosures of which could adversely affect operations.
There was a 25-minute debate in the Dáil on the document, produced by Dr Dermot Nally, former government secretary, Mr Joseph Brosnan, former secretary at the Department of Justice, and Mr Eamon Barnes, former Director of Public Prosecutions. They carried out an examination on the basis of information provided by the Police Ombudsman of Northern Ireland.
The Fine Gael leader, Mr Enda Kenny, said he was not happy with the report because a "key participant" was not interviewed during its preparation.
This was a "major omission" in a report which sought to draw conclusions from seriously conflicting evidence, and he was disappointed the group did not make a greater effort to interview this person.
There appeared to be unresolved conflict in a key area between the information supplied to the group by the PSNI and the Garda.
The Labour leader, Mr Pat Rabbitte, said the Government had to answer a fundamental question on whether it was going to support civil litigation by the families of the Omagh victims against the suspects, and the level of assistance it was going to give.
He quoted the report that the allegations were a direct consequence of and were motivated by concerns arising from the difficulties in which a garda found himself with his superiors and with the criminal law.
The Sinn Féin leader in the Dáil, Mr Caoimhghín Ó Caoláin, said he was unhappy that his party had not received a copy of the report when other Opposition parties had.
