DEPUTY First Minister Michelle O'Neill has described the Police Ombudsman's Operation Greenwich report as "damning".
The 336 page report examined 19 murders and two attempted murders carried out by the UDA/UFF between 1989 and 1993.
In her report Marie Anderson confirmed there was evidence of "collusive behaviour" by some police officers.
The report also concluded that police informers were involved in murder and other serious crime and that records relating to the recruitment and management of informers had been destroyed.
Other findings included a failure by police to make people aware of threats to their lives and evidence that UDR officers passed information to loyalists.
Ms Anderson also said there was a failure to pass on intelligence to police officers investigating attacks.
The circumstances surrounding the murder of several republicans, including elected representatives, were considered by the report.
Sinn Féin Deputy First Minister Michelle O'Neill last night said the "report is damning and confirms what many already suspected, British state forces were working with the loyalist murder gangs that killed these 19 people, among them Sinn Féin councillors Eddie Fullerton and Bernard O’Hagan and a number of party election workers".
"This is further evidence of why the British government wants an amnesty for its state forces and why victims, families, political parties and human rights groups continue to vigorously oppose these plans," she added.
"It's time to address the legacy of the past by implementing the mechanisms agreed at Stormont House in a human rights compliant manner to ensure that families are not waiting any more decades for truth and justice."
SDLP leader Colum Eastwood said the "report into these murders is a clear and total vindication of the families' decades long campaign for truth".
"Those now calling for an end to investigations into serious crimes need to read this report cover to cover," he said.
"They need to understand the impact of those calls and the scale of corruption and criminality that was hardwired into this place through paramilitary death squads and the behaviour of state actors."
East Derry Aontú representative Gemma Brolly, who knows the families of some of those killed, said "those responsible for these murders must be brought to justice" adding her party will "support these families in their demand for justice every step of the way".
DUP Policing Board member Joanne Bunting raised concerns about the ombudsman's report.
"It is deeply concerning that the ombudsman’s finding of ‘collusive behaviours’ is not based on any agreed or independent definition in law indeed this is not the first time such a conclusion has been drawn by that office but not backed up with robust evidence," she said.
East Belfast TUV assembly candidate John Ross also voiced reservations.
"The report published by the Police Ombudsman’s Office which accuses the RUC of “collusive behaviours” paints a totally misleading picture of the security forces," he said.
"In using such a term the office is unfairly blackening the name of the security forces.
"In the way this is being reported it is easy to miss the key fact that police had no prior knowledge of any of the attacks."
