A 65-year-old man held in connection with the murders of 21 people in the 1974 Birmingham pub bombings has been released.
The arrest on Wednesday came just days before the 46th anniversary of the two deadly November 21 blasts which ripped apart the Mulberry Bush and Tavern In The Town pubs.
The individual was arrested at an address in Belfast on Wednesday morning by officers from West Midlands Police assisted by PSNI.
He was arrested under the Terrorism Act and taken to Musgrave Street PSNI custody block in the city, while searches continued at his address throughout the day.
West Midlands Police said he was interviewed under caution at a police station in Northern Ireland but was released after a search of his home was carried out.
Detective Chief Superintendent Kenny Bell, head of Counter Terrorism Policing West Midlands CTU, said: "We are committed to finding those responsible for the terrible murders of 21 innocent victims almost 46 years ago.
"Let me assure families of the victims and the people of Birmingham that we're working relentlessly to find the bombers and bring them to justice."
At an inquest into the bombings last year, a jury concluded a botched IRA warning call on the night led to 21 people being unlawfully killed.
The bungled West Midlands Police inquiry in the immediate aftermath of the bombings led to the wrongful convictions of the Birmingham Six, one of the worst miscarriages of justice in legal history.
They were freed in 1991 after their convictions were quashed.
During evidence given at last year's inquest, an anonymous IRA volunteer named the men he said had been involved in the attacks.
The individual - identified at the hearing only as Witness O - said those who took part were Mick Murray, Seamus McLoughlin and James Francis Gavin, as well as a fourth man, Michael Hayes, who now lives in Dublin.
In a statement issued at the time, Mr Reilly's lawyer Padraig O Muirigh strongly denied allegations he was involved as being "without any foundation".
The arrest came a month after Home Secretary Priti Patel said she would consider holding a public inquiry into the bombings.
Ms Patel also said she wants to visit Birmingham to meet justice campaigners, including Julie Hambleton, whose 18-year-old sister Maxine died in the bombings.
Ms Hambleton, who is part of the victims' families' campaign group Justice 4 The 21, had called the arrest "monumental".