Relatives of those killed in the Lockerbie bombing 27 years ago have welcomed the identification of two Libyans as suspects in the investigation.
The pair are suspected of involvement along with Abdelbaset al-Megrahi - the only person convicted over the 1988 atrocity in which 270 people died.
Scottish prosecutors said they want the suspects, who they have not named, to be interviewed by police.
Megrahi, who was released from jail by the Scottish Government in 2009 on compassionate grounds after being diagnosed with prostate cancer, died in 2012 protesting his innocence.
Scotland's Lord Advocate Frank Mulholland QC recently met US attorney general Loretta Lynch in Washington and they have requested assistance from Libyan authorities for Scottish police and the FBI to interview the two suspects in Tripoli.
Two parents of victims of the atrocity spoke of their delight at the latest development.
Susan Cohen, from New Jersey, whose 20-year-old daughter Theodora was killed in the bombing, told ITV News: "I'm delighted that they are doing this - we the American families have been pressing and pressing for the bombing to be properly investigated.
"I want to make it clear that I think Megrahi did it but the trial was framed too narrowly. The governments have been dragging their feet and they should have been looking for other people involved, because it wasn't just Megrahi."
The families of those killed have been divided over Megrahi's part in the bombing, which has been called into question in a series of books and documentaries.
Dr Jim Swire, who lost his daughter Flora in the bombing, was one of the relatives involved in a recent appeal court action on Megrahi's behalf. Scottish judges ruled that the action should not be allowed.
He told the programme: "Of course I'm pleased (about the identification of suspects). If there is material that shows other people were involved then we want to know.
"We want to know who murdered our families. But the big but for us is we're not satisfied the one man who was found guilty was in fact guilty.
"Therefore we don't know if the Libyan regime was involved in this or not. And we've always said that."
Last month alleged suspects were named in an American television documentary, including Abu Agila Mas'ud. Officials have also previously asked to interview Abdullah al-Senoussi, Muammar Gaddafi's former spymaster, the Associated Press reported.
Both were imprisoned in Libya after the 2011 fall of Gaddafi, and al-Senoussi has been sentenced to death, according to AP. The crimes they have been charged with in Libya are not related to the Lockerbie bombing.
The Pan Am flight was on its way from London to New York when it exploded above Lockerbie, in southern Scotland, on the evening of December 21 1988, killing everyone on board and 11 people on the ground.
Megrahi was found guilty of mass murder following a trial at Camp Zeist in the Netherlands in 2001 and was jailed for life with a minimum term of 27 years.
Last year, exactly 26 years on from the atrocity, the Lord Advocate led a delegation of Scottish law officers who attended a memorial at the Arlington cemetery in Washington.
Mr Mulholland, who addressed the service, said no Crown Office investigator or prosecutor has raised a concern about the evidence in the case and he vowed to track down Megrahi's accomplices.
He has previously said the idea that Megrahi acted alone was ''risible''.
The investigation into the bombing remains a joint one between US and Scottish prosecutors, Police Scotland and the FBI.
A Crown Office spokesman said: "The Lord Advocate and the US attorney general have recently agreed that there is a proper basis in law in Scotland and the United States to entitle Scottish and US investigators to treat two Libyans as suspects in the continuing investigation into the bombing of flight Pan Am 103 over Lockerbie.
"The Lord Advocate has therefore issued an international letter of request to the Libyan attorney general in Tripoli which identifies the two Libyans as suspects in the bombing of flight Pan Am 103.
"The Lord Advocate and the US attorney general are seeking the assistance of the Libyan judicial authorities for Scottish police officers and the FBI to interview the two named suspects in Tripoli.
"The two individuals are suspected of involvement, along with Abdelbaset Ali Mohmed al-Megrahi, in the bombing of flight Pan Am 103 in December 1988 and the murder of 270 people."
First Minister Nicola Sturgeon said she hoped the development would lead to a trial in Scotland.
Amin Khalifa Fhimah stood trial with Megrahi, but was acquitted.
Megrahi lost his first court appeal in 2002 and applied to the Scottish Criminal Cases Review Commission (SCCRC) for a review of his conviction the following year.
A £1.1 million investigation by the body led to a finding in June 2007 of six grounds where it believed a miscarriage of justice may have occurred.
This decision opened the door to Megrahi's second appeal but he dropped it two days before being released from prison in August 2009.