The family of a man beaten to death along with his friend have won High Court permission to challenge a decision not to hold an inquest into their murders.
Relatives of Finbarr McGrillen want a tribunal to examine the double killing which was the focus of a watchdog report highlighting police failures in handling one of the perpetrators.
A judge granted leave to seek a judicial review amid claims a coroner's refusal to hold an inquest breaches their human rights.
Mr McGrillen, 42, and 40-year-old Caron Smyth were attacked at an apartment in the Ravenhill Court area of east Belfast in December 2013.
They had sustained fractured ribs and damaged organs, as well as head, neck and chest wounds consistent with being punched, kicked and stamped on.
Two men subsequently pleaded guilty to the murders - including Ms Smyth's violent ex-boyfriend Sean Hegarty.
Hegarty, 38, who had a more than 70 previous convictions, was arrested days before the killings for allegedly assaulting Ms Smyth.
She told police he had imprisoned her, hit her with a metal bar and threatened to kill her.
Despite officers concluding she was at risk of serious harm and detaining Hegarty, he was subsequently released from police custody.
Three days later he then carried out the murders with his 37-year-old accomplice, Ciaran Nugent.
Both men received life sentences after admitting the killings.
In September last year a Police Ombudsman report listed a catalogue of flaws in how the PSNI handled Hegarty.
He had been released on police bail after PSNI officers, without proper authorisation, allowed him to change the address where he could live.
Those living arrangements did not have an electricity supply needed for an electronic tag supposed to monitor his movements.
Six police officers were disciplined following the report, while another has since resigned due to an unrelated matter.
The McGrillen family, represented by Harte Coyle Collins solicitors, launched judicial review proceedings after a coroner concluded there was no requirement to hold an inquest following the Police Ombudsman's probe.
They claim that decision is in breach of the state's investigative obligations under human rights legislation.
It is understood that relatives of Ms Smyth have also commenced similar proceedings.
The victims' relatives believe an inquest is needed to publicly scrutinise and expose all the circumstances surrounding the murders.
Ruling on the McGrillen family's application, Mr Justice McCloskey set out their argument that the Ombudsman was not fully able to hold state agents to account.
"The applicant makes the case those officers would be compellable witnesses if an inquest were to be held, and the inquest would fill what the applicant says is a gaping chasm in the state investigation into the death," he said.
He confirmed that the challenge had passed the legal test of establishing an arguable case.
"I grant leave to apply for judicial review on the central ground - namely that the coroner's decision is incompatible with the procedural requirements of Article 2 of the Human Rights Convention."
A full hearing is now expected to take place in January.