LONDON — The police have arrested a man in Northern Ireland in connection with the notorious bombing of two pubs in the English Midlands almost a half-century ago, they said Wednesday, an attack whose memory has endured as an emblem of deferred justice and enduring loss.
The bombs exploded within minutes of each other at the Mulberry Bush and at the Tavern in the Town, both in Birmingham, on Nov. 21, 1974, killing 21 people. The identity of the bombers has remained one of the most tangled riddles of an era whose bloodletting still scars its survivors.
The bombings punctuated the decades known as The Troubles when the police and the army struggled to quell an insurgency in Northern Ireland that spilled into mainland Britain with bloody bombings. Thousands of people died in the conflict that drew in the authorities and paramilitary groups fighting for and against Irish unity.
After the Birmingham attacks, the police charged six men with carrying out the bombings, in which around 200 people were wounded. The men, who became known as the Birmingham Six, were jailed in 1975 but released in 1991 when their convictions were overturned. In 1994 the police said there was not enough evidence for further arrests.
In a statement on Wednesday, the West Midlands police said that a 65-year-old man had been arrested under antiterrorism laws at his home in Belfast, Northern Ireland, and that his home was being searched. The man was not identified by name.
While the Good Friday Agreement of 1998, brokered with United States support, created a political settlement to help end The Troubles, memories of the violence persisted and campaigners continued to press for explanations.
Such was the pressure from one group in Birmingham that the authorities reopened an inquest in 2016 into the Birmingham bombings. The group — Justice for the 21 — is still pressing for a broader public inquiry.
Last year the inquest found that the 21 victims had been unlawfully killed by the Provisional Irish Republican Army, or I.R.A. — the most powerful of the groups seeking a united Ireland — but did not identify suspects by name. At the time of the bombings, the I.R.A. did not take responsibility.
Julie Hambleton, whose sister Maxine died in the bombings, called the arrest on Wednesday “the most monumental event” since the release of the Birmingham Six. “It’s welcome news. It’s overwhelming news. It’s tangible progress,” she told the BBC.
But, like other campaigners seeking a broader inquiry, she said the arrest “does not in any way lessen our desire for a full public inquiry.”
“There are wider issues which need to be examined and so much that went wrong, like why six men were arrested for a crime they did not commit,” she said.
Paul Rowlands, whose father John Rowlands died in one of the explosions, called the arrest “a positive step” but said it “does not detract from the fact that we need a public inquiry.”
The memory of those killed in 1974 has been encapsulated in a montage of photographs that has served to illustrate the capriciousness of the killing. The victims include electricians and postal workers, a market porter, several department store workers, and factory and office personnel, among others.
Such memories cement The Troubles deeply into the British political landscape. The freeing of the Birmingham Six — Paddy Hill, Gerry Hunter, Johnny Walker, Hugh Callaghan, Richard McIlkenny and Billy Power — is often referred to by campaigners as one of the most striking miscarriages of justice related to The Troubles.
Mr. Hill, one of the Birmingham Six, told the BBC in 2010: “The one thing about the British public — when they see an injustice they are not afraid to stand up and scream about it — and thank God. We were put into prison just to satisfy and to quell the public outcry and in the end it was the public outcry that got us back out again.”
In recent months, as Britain moves toward its final farewell to the European Union, Northern Ireland’s fortunes have become entwined in the relationship between London and Washington.
The British government of Prime Minister Boris Johnson has drawn up legislation that critics say would rebuild border restrictions dismantled under the Good Friday Agreement. But in Washington, President-elect Joseph R. Biden Jr. has warned Mr. Johnson that the Good Friday Agreement should not be compromised.
“We can’t allow the Good Friday Agreement that brought peace to Northern Ireland to become a casualty of Brexit,” Mr. Biden wrote on Twitter in September. “Any trade deal between the U.S. and U.K. must be contingent upon respect for the Agreement and preventing the return of a hard border. Period.”