The family of Harry Breen have said all their fears have been realised by the tribunal's devastating findings.
They said the officer and his trusted colleague Superintendent Bob Buchanan were betrayed by their counterparts in the Republic's police force.
"An Garda Siochana as a body was held in high regard by Chief Superintendent Breen. He enjoyed a good professional working relationship with various members over the years of his service," solicitor John McBurney said.
"It is tragic that he was betrayed in the manner established by Judge Smithwick whilst he was engaged in significant policing endeavours of importance to the RUC and An Garda Siochana and the jurisdictions both served."
The lawyer for the Breens said the Smithwick report details in the most stark and dramatic fashion the failure by state systems to address the allegations of collusion.
"The family of Chief Supt Breen and many others held deep fears and concerns about the circumstances surrounding the tragic murder and his esteemed colleague Bob," Mr McBurney said.
"Those abiding fears and concerns have now been fully realised with collusion firmly established."
The Breens said they deeply appreciated the courage of some Garda officers and members of the security forces in bringing key evidence to the tribunal.
They asked for time to reflect on the extensive findings the tribunal has uncovered.
"The report has brought enormous clarity to what has been a very shrouded set of circumstances for so many years," Mr McBurney said.
"The knowledge gleaned from the work of the tribunal has brought significant consolation to the family as they come to terms with the treacherous realities, now laid bare, which surrounded the dreadful murder of their loved one."
Banbridge-based solicitor Mr McBurney issued the lengthy statement on the family's behalf and said the tribunal had been faced with a most complex and difficult task.
He praised Judge Smithwick for tireless and painstaking efforts.
Mr McBurney said the Breens deeply appreciated the work the judge had undertaken along with the work of the legal team, administration staff, researchers and investigators.
Northern Ireland's Justice Ministe r David Ford said publication of the report would not be allowed to sour the strong relationship between police services on both sides of the Irish border.
Mr Ford said: "A rogue officer acting outside the law should not result in the loss of trust between the PSNI and An Garda Siochana. Since taking up this office I have worked to build the levels of co-operation between the two services and Alan Shatter and I, as the two ministers, will continue to do this.
"There are many examples on a daily basis of officers from the PSNI and An Garda Siochana working together against those who would try to drag us back to the dark days and I am determined that will continue to ensure the progress made in recent years continues."
Mr Ford said his thoughts were with the Breen and Buchanan families who were having to relive the pain of their loss.
Northern Ireland Secretary Theresa Villiers said: "The report raises some serious concerns which I will need to consider in detail and discuss with the Irish Government. An important point to remember is that levels of cooperation between An Garda Siochana and the PSNI are now at unprecedented levels and are playing a crucial part in combating terrorist attacks in Northern Ireland."
Ms Villiers paid tribute to the two senior officers and their families.
She said: " They were two brave police officers dedicated to upholding the law and protecting the community from terrorism. The publication of the report will be very difficult for their families."