The man accused of making the bomb that blew up the Pan Am 103 flight over Lockerbie in 1988 is now in US custody.
Abu Agila Mohammad Mas’ud Kheir al Marimi is said to be the “third conspirator” behind the attack.
The US Justice Department has confirmed Mas’ud is in custody and said he will make an initial appearance in a federal court in Washington DC.
It is not clear when he will make the appearance.
Some 243 passengers and 16 crew were killed when a bomb, planted on the airliner, exploded at 38,000ft.
Another 11 people were killed on the ground as debris fell on to homes in the town of Lockerbie in Dumfries and Galloway.
It remains the deadliest terror attack on British soil.
The only person to have been convicted over the atrocity was Abdelbaset Ali Mohmed al Megrahi, who was jailed for life in 2001 and released on compassionate grounds in 2009 after being diagnosed with cancer. He died in 2012.
The Scottish authorities said: “The families of those killed in the Lockerbie bombing have been told that the suspect Abu Agila Mohammad Mas’ud Kheir al Marimi is in US custody.
“Scottish prosecutors and police, working with UK government and US colleagues, will continue to pursue this investigation, with the sole aim of bringing those who acted along with al Megrahi to justice.”
In 2020, Mas’ud was charged by William Barr, the US attorney general, with being the third person involved in the terrorist attack.
At the time, he was said to be in Libyan custody and Mr Barr said US authorities would work “arm in arm” with their Scottish counterparts.
“Let there be no mistake, no amount of time or distance will stop the US and our Scottish partners from pursuing justice in this case,” Mr Barr said.