Fifteen people died and 17 others were injured when a bomb left on the North Queen Street bar's doorstep exploded causing the building to collapse.The attack was one of the worst in terms of lives lost in Northern Ireland prior to the 1998 Omagh bombing.The UVF were blamed for the attack and one man was convicted of all 15 murders in 1978.On Wednesday, a 75-year-old man was detained by police in east Belfast. He was taken to Antrim Serious Crime Suite for questioning - and was released unconditionally later the same day.The bombing had initially been wrongly presented by the RUC as an accidental 'own goal' by the IRA but a Police Ombudsman's report into the bombing found police bias meant the atrocity was not properly investigated.Following the Police Ombudsman's report in 2011, the Chief Constable Matt Baggott undertook a review of the RUC investigation to identify any possible opportunities for further investigation.A review process which initially involved the Historical Enquiries Team, and more recently detectives in Serious Crime Branch, was carried out which has identified investigative potential, police have said.The officer leading the renewed investigation, Detective Chief Inspector Justyn Galloway, said: "Despite the passage of time, there remain a number of opportunities to make progress."We will do our best to develop these lines of enquiry as thoroughly and quickly as possible."At the same time, I would ask those individuals who know who was involved in this attack on 4 December 1971 to talk to us."Much has changed in the four decades since this terrible atrocity but the families of the victims and survivors continue to suffer."I would ask that anyone with information or suspicions about this bomb attack to come forward."The attack happened as the conflict began to deepen and victims' relatives have spearheaded a long-running justice campaign.A permanent memorial to the atrocity remains at the junction of North Queen Street and Great George's Street and the families of the victims have been advised of the latest development.Anyone with information can contact detectives on 028 9180 1507 or email zMIT3@psni.pnn.police.uk.Alternatively, information can be passed anonymously to the independent charity Crimestoppers on 0800 555 111.