A man (75) has been arrested by detectives investigating a Belfast pub bombing which killed 15 people.
The attack at McGurk's in the city in 1971 happened as the Northern Ireland Troubles began to deepen.
Victims’ relatives have spearheaded a long-running campaign for justice over such incidents.
The suspect was detained after the Police Service of Northern Ireland reopened its investigation.
The officer leading the renewed inquiry, Detective Chief Insp 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 inquiry 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.”
The attack was carried out by loyalist paramilitary group the Ulster Volunteer Force (UVF), even though in the immediate aftermath of the attack the IRA was blamed for planting the bomb.
In February 2011 the Northern Ireland Police Ombudsman published a report which said the original Royal Ulster Constabulary (RUC) investigation was biased.
Later, the independent Historical Enquiries Team (HET) of detectives, which is probing more than 3,000 unsolved conflict killings, and more recently the PSNI, reviewed the case for new leads.
In 1978 a member of the UVF, Robert Campbell, was convicted of the murders and attempted murders of those in McGurk’s Bar.
The 75-year-old was detained in East Belfast and taken to Antrim police station.
Press Association