A judge has said he will compel the PSNI's Chief Constable to complete an investigation into the activities of the so-called Glenanne Gang, which has been linked to up to 120 murders.
The gang was based at a County Armagh farm.
It included members of the UVF, RUC and UDR.
A report into its alleged activities by the Historical Enquiries Team (HET) was 80% completed before the police unit was disbanded.
The Police Service of Northern Ireland (PSNI) has not completed or published the report.
Earlier this year, a judge ruled that the PSNI had breached the human rights of the victims' families and it had frustrated "any possibility of an effective investigation".
In the High Court in Belfast on Tuesday, Mr Justice Treacy said he would grant what is called "an order of mandamus" that compelled the Chief Constable to conduct a lawful investigation, and complete and publish an overarching thematic report.
He also said witnesses and those bereaved by the gang are dying without achieving any closure on suspected state collusion.
"The very sad inescapable fact is that while these debates rage on at huge public expense, the victims' families languish with no end in sight and the ever increasing realisation that nothing much may happen in their lifetime," he said.
The Glenanne Gang is believed to have been responsible for the murders of 33 people in the 1974 Dublin and Monaghan bombings .
It has also been linked to a number of other atrocities, including the 1975 Miami Showband Massacre in which three members of the popular group were shot dead.
The judge has given the PSNI a week to confirm that there are no minutes or documents about the decision not to complete the HET investigation.
Welcoming the judgement, Sinn Féin's Linda Dillon said: "I am calling on the PSNI to comply with the judgement and provide the necessary resources and facilitate an effective and independent investigation so that the families can get access to truth and justice."