Former US intelligence contractor Edward Snowden's stop in Moscow is an unexpected windfall for the Russian secret services even if it risks worsening the already strained relations between the Kremlin and Washington.
Snowden's sensational revelations on the electronic surveillance carried out around the world by the United States present great interest for Russian intelligence officials, who will have seized the opportunity to question him, experts said Monday in Moscow.
The location of the US fugitive is now a mystery. He was not on board Monday's flight to Cuba on which he was booked, and his current whereabouts have not been confirmed amid speculation he could still be in Russia or have flown to another destination.
"Russian intelligence and counter-intelligence will have a lot to ask such a well-informed person. I have no doubt that this will be done," a Russian special services veteran told the Interfax news agency on Sunday on condition of anonymity.
"I am sure that Snowden will have had a busy evening and a sleepless night," the source added of the American's reported stayover Sunday night in the transit zone of Moscow's Sheremetyevo airport after landing from Hong Kong.
"Snowden presents a lot of interest for the FSB (security service). He can give information on technical aspects of intercepting data," said Russian security expert and commentator for the Novaya Gazeta newspaper Pavel Felgenhauer.
"A debriefing in the presence of technical specialists takes a lot of time," Felgenhauer told AFP, suggesting that interviews with Russian secret services could take place in a third country.
"They can't get it in one short conversation, as they usually debrief defectors. He was not a special services operative, he cannot talk about their methods. He can give what he recorded," security services expert Irina Borogan of Agentura.ru website told AFP.
Since June 5, Snowden has exposed information on collecting data on phone calls and Internet communications by US intelligence agencies and there is little question that his knowledge could be valuable to the Russian secret services.
"I hope that in one way or another, in any case, Snowden will have to share his information, including facts about electronic espionage by the United States against Russia," Igor Korotchenko, editor of National Defence journal, told Rossiya 24 television.
He added that Russia's SVR (Foreign Intelligence Service), FSB and GRU (military foreign intelligence service) "are headed by professionals" and will not reveal any information on possible contacts "for the next 50 years."
Documents leaked this month by Snowden to the Guardian newspaper showed that Britain spied on foreign delegates at the 2009 London G20 meetings, including then Russian president Dmitry Medvedev.
But whatever Russia gains from speaking to Snowden, on a diplomatic level the fugitive's case will exacerbate a deep-freeze in the already tense relations between Moscow and Washington.
Russia and the United States take opposing positions on a long list of issues including the conflict in Syria and the deterioration of the human rights situation in Russia.
While Snowden on Sunday was believed to be in the transit zone in Moscow, Washington asked Moscow to expel him and send him to the United States.
"We expect the Russian government to look at all options available to expel Mr. Snowden back to the US to face justice for the crimes with which he is charged," said National Security Council spokesperson Caitlin Hayden.
Russia did not respond to the US demand, after saying several days before that if Snowden made an asylum request, it would be considered.
Snowden checked in but failed to board an Aeroflot flight to Cuba on Monday afternoon, from which he was expected to continue to Ecuador.
"Relations between Russia and the United States are so bad that I don't know what you could do to make them worse," Viktor Kremenyuk, deputy director of the USA and Canada Institute, told AFP.
"Against the background of other problems in Russian and American relations, this won't have an effect," said Felgenhauer.
"But if he stays, it will have serious negative consequences for our countries' relations."