The sole survivor of the Kingsmill massacre is taking legal action in a bid to have two IRA men suspected of involvement in the murders publicly named.
Alan Black wants the High Court to order that the identities of the alleged perpetrators must be revealed at an inquest into the 1976 atrocity.
The move comes amid rumours that at least one of those connected to the killing of ten Protestant workmen was a British state agent.
That suspect, who has since died, was an ex-soldier linked to more than 30 murders in total, according to legal papers.
Mr Black, 76, was shot 18 times and left for dead alongside the lifeless bodies of his ten friends after the IRA ambushed their minibus near Kingsmill, Co Armagh.
Gunmen ordered the victims out of the van, lined them up and instructed the only Catholic to leave before opening fire.
No-one has ever been convicted for one of the worst outrages committed during the Troubles.
An ongoing inquest into the shootings has heard two suspects linked to the massacre later received controversial on-the-run 'comfort letters', informing them they were not wanted by police.
The coroner overseeing the tribunal has so far declined to name those individuals, saying he would consider arguments on what was described as a "complicated" issue.
With the suspects currently referred to by ciphers, Mr Black has taken preliminary steps towards seeking a judicial review of that stance.
Explaining his reasons for the legal challenge, he expressed deep concerns at how the matter has been handled.
"I have a debt to pay to my pals, I have carried this survivor's guilt around for 44 years," he said.
"I have to do everything in my power to get the truth for all the families. We don't just deserve it, we demand it."
Mr Black's lawyers insisted the identity of one suspect, S97, is already in the public domain.
He was also allegedly connected to the killings of three members of the Royal Highland Fusiliers in Belfast in March 1971, and bomb attacks which claimed the lives of 18 British soldiers at Narrow Water, near Warrenpoint, Co Down in August 1979.
According to Mr Black's legal team, the lack of investigation into allegations surrounding S97 has fuelled rumour and suspicion that he was working as a state agent.
Even though naming both suspects has not been ruled out, lawyers claim the current situation is causing distress to relatives of the Kingsmill victims.
A pre-action letter sent on behalf of Mr Black stated: "He will seek an order from the court that the coroner lifts the ciphers so that the names of the alleged perpetrators can be known and their role, if any, in the deaths at Kingsmill (and near fatal attack on the applicant) can be effectively investigated during the course of the inquest."
His solicitor, Kevin Winters, acknowledged the sensitive and complex issues facing the coroner.
"The decision to take legal action isn't taken lightly, but really it comes on the back of a number of developments, including a recent BBC Spotlight documentary implicating one man in the killings," Mr Winters explained.
"Mr Black has heightened suspicions around what happened in 1976, especially in relation to alleged state collusion.
"This has been a difficult decision for him, but he feels he has no option given what he feels is mounting, rather than diminishing, suspicions on what happened.
"He is 76 now and he just feels he has little option to get to the truth."
The proposed challenge also centres on a decision to refuse Properly Interested Person (PIP) status to Mr Black at the hearing.
Correspondence sent in response from the Coroner's Service pointed to assurances that he will be given a full opportunity to participate as a key witness, and can invite the inquest to pursue a particular line of inquiry.
Any legal challenge is to be fully contested, with all criticisms rejected as "entirely baseless".
The letter also stated: "The issue of lifting cipher numbers allocated to deceased suspects has been the subject of full written and oral argument in the inquest proceedings and remains to be determined by the Coroner."