Police documents about an IRA bombing that killed 12 people at a Northern Ireland hotel "have disappeared", victims' relatives have claimed.
La Mon House, a hotel in countryside outside Belfast, was targeted in one of the most horrific attacks of the Troubles, with many of those killed in February 1978 burned beyond recognition by a fireball.
Interviews with IRA men, original papers from up to 100 detectives and notes about a warning call and a car used by the bombers have not been recovered by independent investigators reviewing the case, according to the victims' families.
They have now renewed calls for a full public inquiry into the bombing.
A statement issued by the families read: "It would appear to the victims that key documents were removed from the files with the view to protecting IRA members who today may be involved in the peace process at the highest level.
"This case, in common with other major investigations, appears to show that the will to uncover the truth has been curtailed for fear of destabilising the current political process."
West Belfast man Robert Murphy was sentenced to life imprisonment for manslaughter in 1981. He was released in 1995 and died in 2006. A second man was acquitted.
The call for a new inquiry followed a review of the police investigation by the independent Historical Enquiries Team which delivered a report to the families.
The statement went on: "It is most disturbing that the investigation of an attack described by the RUC as horrific and indiscriminate mass murder has been hampered because key documentation has been mislaid.
"Considering the circumstances of this horrendous crime and the certainty of the involvement of the IRA, the victims are appalled by the absence of diligence shown by the Royal Ulster Constabulary/Police Service of Northern Ireland in ensuring the preservation of all information related to this investigation and also calls into question the integrity and thoroughness of the whole historical inquiry process."