Whelan, Felgenhauer told DW, doesn't seem like a typical American spy; he pointed out that the 48-year-old global security director for a United States auto parts company has never even held diplomatic immunity. At the time, he was identified only as an American.
Russia's Foreign Ministry has confirmed the United States detained a Russian citizen to face charges of attempting to export arms illegally and money laundering, just a day after an ex-marine was arrested in Moscow on spying charges.
Mr Whelan's family said he was attending a wedding, while Russian Federation said he was "caught spying" in Moscow.
On Thursday, Whelan, security chief for worldwide auto parts manufacturer BorgWarner, was formally charged with espionage and could face 20 years in prison.
Paul Whelan holds four passports - US, UK, Canadian and Irish - as he was born in Canada to British parents, moved to the US and served in the marines, and has an Irish grandfather. Britain, Canada and Ireland have applied for consular access to him.
After his discharge, Whelan returned to his job in the temporary staffing company Kelly Services, based in Troy, Michigan, where he had worked since 2001 in the IT department until taking the leave of military absence. It was during his military service that he first took a trip to Russian Federation. But his military career ended with a court martial in 2008, when he was convicted on charges that included attempted larceny and dereliction of duty. Whelan's family says they knew nothing about these convictions.
The news that Paul Whelan holds citizenship in four countries brings worldwide pressure on Russian Federation from several fronts.
Whelan visited Russian Federation regularly since his first trip there in 2006. He has also reportedly set up a social media account on the Russian equivalent of Facebook, VKontakte.
The Russian Foreign Ministry has issued a warning about what it describes as a "hunt on our citizens", urging travelers to be cautious.
Russia's FSB state security service detained the 48 year old in Moscow last Friday on suspicion of spying.
But Moscow hit back at that suggestion.
But Russian Deputy Foreign Minister Sergei Ryabkov said Saturday that discussing a possible swap involving Whelan and Maria Butina would be premature because Whelan hasn't been formally charged, according to Russian news agencies.
The Russian Embassy in Washington is seeking access to Makarenko, and the ministry is demanding an explanation for the arrest.
Documents at the time of indictment said Makarenko, who the USA said lived in the Pacific city of Vladivostok, would order items such as night-vision scopes - which are subject to a license - and have them shipped to an associate in Florida, Vladimir Nevidomy, who then sent them on to Makarenko, sometimes concealed in household goods shipments.
The Marine Corps is providing details on the court-martial of an American man who has been detained by Russian Federation on spying charges.
Speaking to the Press Association from Newmarket, Ontario, Mr Whelan's twin brother David said: "In the short-term the thing we would appreciate most from the UK Government and are certain that it's going to happen - we're not questioning any will on their part after Mr Hunt's statement - is that they will keep an eye on Paul and assist the U.S. and the other two countries to maintain him in good health until we can get him home".
A document filed by the US District Court for the Northern Mariana Islands on December 31 requests Makarenko's transfer to the Southern District of Florida.
Foreign Secretary Jeremy Hunt said individuals should not be used as diplomatic pawns, as Mr Whelan also holds a British passport. David Whelan recounts how his twin used to tell people about his work: "He was pointing out some problems [at a plant] like they had open windows, like on the second floor - or a half floor up or something".