Relatives of those killed in the 1971 McGurks bar Bombing say they'll hand over newly uncovered evidence to the police ombudsman today.
Fifteen people were killed in the blast in North Belfast.
The bombing was carried out by the UVF, but had initially been presented by the RUC as an accidental ''own goal'' by the IRA.
Speculation mounted at the time that the dead might have included IRA members who were carrying the device.
A Police Ombudsman's report in 2011 said RUC officers had shown an "investigative bias" with the original misattribution of blame.
However, the PSNI's then-chief constable Matt Baggott refused to accept that particular finding by the ombudsman and a subsequent probe by the police's Historical Enquiries Team concluded there was no such bias.
George Hamilton, the current Chief Constable, said he had reviewed the case earlier this year and, as a consequence, changed the PSNI's official position.
Families claim to have found a new document which shows the original blast zone as being at the door of the pub, and not inside.
It will be presented to Dr.Michael Maguire this morning in the hope he scraps the original HET report and recommends a new Inquest .