Moussa Koussa is the ultimate Libyan insider, a one-time intelligence chief and the keeper of Moammar Gadhafi's darkest secrets.
Now that the ex-foreign minister has fled Tripoli and landed in Britain, Western diplomats and intelligence officials were pressing him Thursday for the details that could help oust Gadhafi from power.
Koussa, 62, is the highest ranking member of the secretive regime to quit so far. He had been a longtime aide throughout Gadhafi's 42-year rule and his apparent defection raised hopes among some in the West that he could hold key details that could be used to bring down Libya's leader.
In Washington, National Security Council spokesman Tommy Vietor said Koussa could likely "provide critical intelligence about Gadhafi's current state of mind and military plans."
A second senior Libyan official also announced he had quit Thursday in a statement posted on several opposition websites. Ali Abdel Salam al-Treki _ Libya's former envoy to the U.N. and also a former foreign minister _ confirmed his defection as rumors swirled that other key aides were also preparing to abandon Gadhafi.
British Prime Minister David Cameron urged those who he termed "Gadhafi's henchmen" to follow the example of Koussa, who flew into Britain from Tunisia late Wednesday and announced he had quit his post. Cameron declined to offer details of initial talks between British officials and Koussa, but said his decision to abandon Tripoli was telling.
"I think it does show a huge amount of decay, distrust and breakdown at the heart of the Gadhafi regime," Cameron told reporters in London.
Abdel Moneim al-Houni, Libya's former Arab League representative and among the first wave of Libyan diplomats who defected, said Koussa's exit hinted that Gadhafi's inner circle is close to collapse.
"Koussa is one of the pillars of Gadhafi's regime since the 1970s. His defection means that he knew that the end of Gadhafi is coming and he wanted to jump from the sinking boat," al-Houni said.
Cameron insisted that whatever information Koussa does offer, he won't be granted immunity from prosecution for past crimes. "There is no deal of that kind," Cameron said.
Scottish prosecutors confirmed they hope Koussa can shed light on the 1988 bombing of Pan Am Flight 103 over Lockerbie, Scotland, which killed 270 people _ most of them Americans. Libya acknowledged responsibility for the terrorist attack in 2003, and opposition leaders have long claimed Koussa was closely involved.
Scotland's First Minister Alex Salmond said that Koussa "may well have important information to reveal which can assist what has always remained a live investigation."
Libya's government confirmed Koussa had resigned, but claimed he had been given permission to travel to Tunisia because he was suffering with diabetes and high blood pressure. Government spokesman Moussa Ibrahim also insisted Koussa's decision was not a snub to Gadhafi.
Britain's Foreign Secretary William Hague said Koussa was being debriefed by officials at a secure location in Britain., but did not provide further details.
London-based Libyan dissident Salem Gnan suggested Koussa could provide a trove of information on Gadhafi's inner circle, the country's shadowy past and the dictator's increasing desperation.
Koussa is Libya's "black box and curator of Gadhafi's top secrets," Gnan said. "He will uncover it all. He has got all the names, the documents and the information."
Noman Benotman, a former Libyan radical who has family connections to Koussa, said the ex-minister would be able to explain the extent to which Tripoli was involved in terrorism and disclose whether Libya still has supplies of sarin gas and other chemical weapons. "He understands the regime and critically, he understands all the players," Benotman said.
Britain's Foreign Office did not deny claims in British press reports that it was in contact with as many as 10 other regime officials who were considering whether to defect.
Hague declined to offer details to reporters, saying it would not be "helpful to advertise" whether or not other regime loyalists planned to quit.
Diplomatic officials said no other nations had been granted access to Koussa so far, but explained that the ex-minister was talking to Britain voluntarily and not being held under any form of detention.
Susan Cohen, of Cape May Court House, New Jersey, whose daughter died in the Pan Am bombing, said she hoped Koussa would offer information to help prosecute Gadhafi over the airliner killings.
"Moussa Koussa is a terrible man, he has lots of blood on his hands," she said. "He could be said to be the architect of the Pan Am 103 bombing. But the major villain, the absolute villain in all of this is Moammar Gadhafi. These other guys are just evil henchmen."
David Hartwell, a Middle East analyst with the diplomatic and military publication Jane's, said Koussa's knowledge of Libya's military strength, and the waning solidarity among Gadhafi's aides would make him a valuable asset over the coming days and weeks.
But he warned that "Koussa's murky past and alleged connection to the deaths of many overseas Libyan dissidents and possible links to the Lockerbie attack pose awkward moral and legal questions in the longer term."
Koussa was expelled from Britain in 1980 after giving an interview in which he advocated the use of violence to silence critics of Libya's government in Britain. However, he was deeply involved in returning Libya into the international fold in the 1990s after terror attacks tainted the North African country's reputation.
Britain restored diplomatic relations in 1999, and Gadhafi later announced he was dismantling his nuclear weapons program, a step that prompted the United States and Europe to lift sanctions.
Guma El-Gamaty, a spokesman in Britain for the Benghazi-based Interim National Council _ the political wing of Libya's rebel forces _ hailed Koussa's resignation, but said he would not be welcomed into the opposition because of his past.
Katarina Kratovac and Maggie Michael in Cairo, Paisley Dodds, Danica Kirka, Gregory Katz and Cassandra Vinograd in London, Hadeel al-Shalchi in Tripoli and Geoff Mulvihill in Trenton, New Jersey, contributed to this report.