The US has announced charges against a Libyan suspected of making the bomb that blew up Pan Am Flight 103 over Lockerbie, Scotland, in 1988.
Abu Agila Mohammad Masud has been charged with terrorism-related crimes, Attorney General William Barr said on Monday, 32 years on from the atrocity.
The deadly bomb attack on the Boeing 747 killed 270 people, including 190 American citizens.
Prosecutors will seek the extradition of Mr Masud to stand trial in the US.
The attack on the London to New York flight remains the deadliest terrorist incident ever to have taken place in the UK, and the second deadliest air attack in US history.
Eleven people on the ground in Scotland were also killed. The victims included 35 study abroad US students who were returning home for Christmas.
The new charges bring Mr Barr's role in this lengthy terrorism investigation full circle, as he was also US Attorney General when charges were first announced against two Libyan suspects in 1991.
Back then, serving under President George H W Bush, Mr Barr tasked his criminal division head Robert Mueller to look into the bombing. Mr Mueller is now best known for leading the inquiry into Russian meddling in the 2016 presidential election.
Both Mr Barr and Mr Mueller have taken part in remembrance events with families over the years.
Police Scotland's chief constable, Iain Livingstone, said the charges were a "significant development" and that they will "continue to work closely" with the US and other international authorities. He said it was "inappropriate to comment further" at this time.