Abu Agila Mohammad Masud was charged by the United States two years ago for the Lockerbie bombing, in which Americans made up a majority of the victims
After arriving in the United States he was taken to a Justice Department facility in Alexandria, Virginia for initial processing, where his mug shot was taken.
On Monday afternoon at 1800UTC he will appear in federal court in Washington for an initial hearing.
On Sunday Scottish prosecutors announced that he was in American hands, but provided no details how he had been transferred from Libya.
Masud had previously been held in Libya for his alleged involvement in a 1986 attack on a Berlin nightclub.
Only one person has so far been convicted for the bombing of Pan Am flight 103 on December 21, 1988, which remains the deadliest terror attack on British soil.
The bomb on board the Boeing 747, which was flying in December, 1988 from London to New York City, killed all 259 people on board and 11 on the ground, the deadliest ever militant attack in Britain.
A Justice Department spokesperson confirmed to Reuters on Sunday that the United States has custody of the suspect. Mas'ud is expected to make his initial court appearance in a federal court in Washington.
The families of those killed in the Lockerbie bombing have been told the suspect is in U.S. custody, a spokesperson for Scotland's Crown Office and Procurator Fiscal Service (COPFS) said on Sunday.
Details about the timing of the hearing will be forthcoming, the spokesperson added.
Court documents described Mas'ud as an expert bombmaker who joined Libya's External Security Organization intelligence service in the 1970s and took part in a number of operations outside Libya, reaching the rank of colonel.
A military source in the Libyan city of Misrata said Mas'ud had been flown from the airport there. Reuters could not immediately establish when.
In 1991, two other Libyan intelligence operatives were charged in the bombing: Abdel Baset Ali al-Megrahi and Lamen Khalifa Fhimah.
Megrahi was found guilty of the bombing and was jailed for life in 2001. He was later released because he was suffering from cancer and died at his home in Tripoli in 2012.
Fhimah was acquitted of all charges, but Scottish prosecutors have maintained that Megrahi did not act alone.
In 2020 the United States unsealed criminal charges against Mas'ud, a suspected third conspirator, adding he had worked as a technical expert in building explosive devices.
At the time of the bombing, U.S. investigators uncovered evidence that one of the possible suspects went by the name of "Abu Agela Masud," but were unable to locate him, according to a sworn statement by an FBI agent in support of the government's criminal complaint.
Decades later, the FBI obtained a copy of a Sept. 12, 2012, interview of Mas'ud conducted by a Libyan law enforcement officer while he was in custody there.
During the interview, Mas'ud "admitted to building the bomb that brought down Pan Am Flight 103 and to working with Megrahi and Fhimah to execute the plot," the FBI agent's statement says.
Mas'ud also told the interviewer he was involved in other similar plots, and said the bombing was ordered by Libyan intelligence leadership.
He also said former Libyan leader Muammar Qadaffi, who was killed by rebels in October 2011, "thanked him and other members of the team for their successful attack on the United States."
The agent who filed the statement said the FBI was able to corroborate Mas'ud's confession through the course of its investigation.
The handover of Mas'ud for trial in the West prompted infighting among Libyan politicians, who are split between a parliament based in the east of the country and a Government of National Unity in Tripoli.
Some eastern lawmakers accused Prime Minister Abdulhamd al-Dbeibah of doing Washington's bidding despite the lack of an extradition treaty.
