Scottish prosecutors have asked to interview Moussa Koussa about the Lockerbie bombing after the Libyan foreign minister and spy chief defected to Britain.

The request from the Crown Office in Scotland follows demands from Libya's rebel leadership for Koussa to be returned to Libya for trial for murder and crimes against humanity after Muammar Gaddafi is toppled from power.

Moussa Koussa. Photograph: Mohamed Messara/EPA

William Hague, the British foreign secretary, has said the UK is not offering Koussa immunity from prosecution.

The Crown Office in Edinburgh has said it is formally asking for its prosecutors and detectives from Dumfries and Galloway police to question Koussa about the 1988 bombing. "We have notified the Foreign and Commonwealth Office that the Scottish prosecuting and investigating authorities wish to interview Mr Koussa in connection with the Lockerbie bombing," it said.

"The investigation into the Lockerbie bombing remains open and we will pursue all relevant lines of inquiry."

Dumfries and Galloway police, which investigated the Lockerbie case, has confirmed its detectives are keen to interview Koussa.

It remains unclear what role Koussa played when Pan Am flight 103 was blown up over Lockerbie in December 1988, killing 270 passengers, crew and townspeople. He later emerged as head of Libyan intelligence services.

Koussa's defection provides Britain with an unparalleled source of intelligence on the state of the Libyan ruler's inner circle. The Crown Office interview request will further complicate the position of the UK government, which is immediately concerned with using his defection to intensify pressure on Gaddafi and his close allies, and to provide intelligence to the rebellion.

Senior figures in the Lockerbie case – including Jim Swire, whose daughter Flora was killed in the attack, and Professor Robert Black, a lawyer and architect of the trial of two Libyans accused of the atrocity – have said they believe Koussa might have significant information about Libya's role.

Koussa was pivotal in the negotiations to hand over the two suspects – Abdelbaset al-Megrahi and Al-Amin Khalifah Fhimah – for trial at Camp Zeist in the Netherlands in 2001. He oversaw Libya's negotiations to pay billion of pounds in reparations for the attack.

The Libyans' consistent denial of responsibility for the Lockerbie bombing has been repeatedly rejected by the UK and US governments, and Scottish prosecutors.

Swire, from UK Families of Pan Am Flight 103, and Black, emeritus professor of Scots law at Edinburgh University, have said they believe Megrahi is innocent. He remains the only man convicted of the bombing.

As Libyan foreign minister, Koussa met Foreign Office and Scottish government officials at least twice in 2008 and 2009 to negotiate Megrahi's release from Greenock prison. Koussa visited Megrahi in jail. Megrahi's lawyer, Tony Kelly, has declined to comment on the latest developments.

Swire said the weight of evidence pointed to Syria as the main culprit but "within the Libyan regime [Koussa] is in the best position of anyone other than Gaddafi himself to tell us what the regime knows or did. He would be a peerless source of information".

Detective Superintendent Mickey Dalgliesh, who is in charge of the Lockerbie case at Dumfries and Galloway police, said the Crown Office request to interview Koussa was "in line with our position that the investigation into the Lockerbie bombing remains open and we are determined to pursue all relevant lines of inquiry".

Alex Salmond, the first minister of Scotland, said the Crown Office request was "an extremely positive step forward". Koussa "may well have important information to reveal which can assist what has always remained a live investigation".

"Megrahi was convicted by a Scottish court on the basis that he was a Libyan intelligence officer and that he did not act alone. This welcome announcement by the Crown Office, and the intention of Dumfries and Galloway police to interview him, will hopefully lead to further information and lines of inquiry coming to light about the Lockerbie atrocity," he said.

Libya rebels insist on prosecuting Koussa



Mustafa Gheriani, a spokesman for the Libyan revolutionary council, has said the rebels are not bent on revenge against the regime's officials but some of Gaddafi's closest associates "have a lot of blood on their hands" and must stand trial.

Speaking from the rebel capital, Benghazi, Gheriani said Koussa had been partly responsible for assassinating opposition figures in exile, murderous internal repression and Lockerbie.

"We want to bring him to court," Gheriani said. "This guy has so much blood on his hands. There are documented killings, torturing. There's documentation of what Moussa Koussa has done. We want him tried by Libyan people.

"I believe once we have our government 100% in control in Libya, things are normalised, we want him tried here. I think international law gives us that right."

Gheriani said it was up to Britain to decide whether to arrest Koussa in the meantime. Koussa's arrival in London was evidence that Gaddafi's regime was "starting to crumble". He expected other senior officials to follow.

"He is a very, very major person to defect. Gaddafi trusted him more than some of his sons. Now Gaddafi doesn't even trust his own people any more," Gheriani said.

Gheriani said a senior military official in Kufra, Colonel Saleh al-Zaroug, had defected to the rebels. He had served in an army division commanded by one of Gaddafi's sons. The defection was impossible to confirm.

Hague said Koussa had come to the UK on a private plane from Tunisia having left Libya of his own free will. "Gaddafi must be thinking to himself: 'Who will be the next to walk away?'" Hague said.

It would not be "helpful to advertise" whether other senior members of the regime planned to quit, Hague said, but he believed it was likely that many opposed Gaddafi's actions. Koussa was in a secure place in the UK and talking voluntarily to British officials, including staff at Britain's Tripoli embassy now based in London.