A COVER-up of Fr Niall Molloy's murder was "aided and abetted by omerta-style collusion between the most powerful forces in the State," a Fine Gael deputy told the Dail.
Michael Creed TD named those forces as "the senior political establishment, the judiciary, the church, senior medical personnel and the gardai".
He said it was "imperative" that Justice Minister Alan Shatter now establish an independent judicial inquiry.
A native of Roscommon, Fr Molloy (52) was brutally beaten to death in the mansion of Therese and Richard Flynn in Clara, Co Offaly in July 1985.
Senior Fianna Fail members, including a household name, were in the house on the evening of the murder.
Richard Flynn was charged with manslaughter, but Judge Frank Roe cut the trial short and directed the jury to acquit him after less than four hours. It later emerged that the judge knew the parties involved and should not have heard the case.
Another individual, not Richard Flynn, is believed to have killed Fr Molloy.
An extensive probe by the Irish Independent resulted in a new probe by the Cold Case Unit in December 2010, but two years on, the Molloy family and many others are deeply disappointed by its lack of progress.
Mr Creed said: "I believe gardai investigating gardai – which is effectively what the Cold Case Unit is doing – is not an appropriate way to proceed."
He was joined in his calls by Fine Gael TD for Carlow-Kilkenny, John Paul Phelan.
"I am not one who is taken by conspiracy theories but the whole evidence as presented seems quite clearly to suggest that there are more than just freak events occurring here," he said. "There is some level of collusion, some level of cover-up by very powerful influences in our society."
Applauding what he called the "great and brave work" done by this newspaper on the case, Deputy Finian McGrath (Dublin North Central) said: "The country and the citizens of this State deserve the facts".
Meanwhile, Roscommon County Council voted in favour of a motion calling for a Commission of Inquiry into the Fr Molloy case.