A brother of former INLA chief Dominic McGlinchey has accused authorities in Dublin of denying his family justice.
Sinn Féin councillor Sean McGlinchey made the comments after High Court action was lunched in an attempt to force gardai to open a fresh investigation into the separate murders of Mr McGlinchey and his wife Mary.
Originally from south Derry, ex-INLA 'chief of staff' Dominic McGlinchey was shot dead in Drogheda, Co Louth, on February 10 1994.
A former member of the IRA, in an 1983 interview he claimed to have killed 30 people during the Troubles.
His wife Mary was gunned down while bathing her young children at their home in Dundalk, Co Louth, on January 31 1987.
Among concerns raised by Sean McGlinchey is that a bath said to have been taken from the murder scene by authorities and stored at the back of Dundalk garda station was later used as a "flower box".
He also said that correspondence sent to gardai about the case along with requests for a meeting with the commissioner have been ignored.
It has previously been reported that a file into the murder of Mary McGlinchey cannot now be found.
The couple's son, also Dominic, witnessed the murder of both his parents.
He recently launched judicial review proceedings in relation to both murders against the office of the Commissioner of An Garda Siochána and Minister for Justice, Helen McEntee.
The current garda commissioner is former PSNI deputy chief constable Drew Harris.
Mr McGlinchey, a Sinn Féin councillor at Causeway Coast and Glens council, said he is "horrified even at this stage of the peace process" by the approach of authorities in Dublin.
"There are many victims and survivors from the recent conflict on this shared Island that still are denied justice," he said.
"There is no monopoly on victimhood and there should never be any superiority with survivors, however my nephew is still denied any form of justice or access to achieving the truth into the gruesome and heinous murders of his parents."
Mr McGlinchey said that before his brother was murdered an unsuccessful attempt was made on his life at Ardee, Co Louth, during a 16th birthday party for his son Declan, who died in 2015.
Read more:Who are the UVF?
The loyalist gang behind the failed murder bid is believed to have included former UVF and LVF commander Billy Wright, who Mr McGlinchey described as a "suspected RUC Special Branch agent".
Read more: Who was Billy Wright?
Mr McGlinchey said he was "disgusted" that letters sent by his nephew's legal team to gardai in Co Louth and the garda commissioner over the past two years regarding the status of the investigation and missing exhibits have gone unanswered.
"To ignore such legal letters and the invitation of a meeting is disgraceful," he said.
Mr McGlinchey added that "questions need answered and this situation needs addressed immediately".
The Sinn Féin man said it was "not right or fair" for his still grieving family "to rely on journalists, their sources, or retired Gardaí with a conscience to get drip-fed information over generations".
"The fact that a murder file has vanished should be subject to an investigating in itself and the family alerted," he said.
"We have even heard suggestions that the bath in which Mary was found in was left at the back of Dundalk Garda Station and after years used as a flower box."
Mr McGlinchey said all his family wants is "access to the truth".
"This is not about retribution or any form of prosecution but rather reconciliation and an opportunity for us to move forward as a family and future generations can be free of the bondage of our past," he added.
The Sinn Féin councillor added that the Dublin government needs to take a "serious and honest look at how they are dealing with legacy matters".
"Forcing my nephew to bring several High Court cases for his parents just to get basic answers and some form of closure is wrong and so hurtful," he said.
"I am now pleading with justice minister in Dublin and all the relevant agencies involved to review this matter immediately, too many years and opportunities have already been lost and we are all entitled to the truth."
Solicitor Ciarán Mulholland, of Mulholland Law, said: "It is incredibly frustrating the double standards on this Island dealing with legacy matters like the cases of Mary and Dominic - south of the border we still have no real police accountability, a dysfunctional coronial system and no similar legal aid system akin to that in the north.
"Therefore victims and survivors in this jurisdiction are ultimately denied access to justice.
"This requires immediate actioned by the government.”
A spokeswoman for An Garda Síochána said it "does not comment on matters before the High Court".
The Department for Justice in Dublin said it "is unable to comment on individual cases".
