The former U.S. Marine that's been charged in Russia on espionage allegations is being held in solitary confinement at the notorious Lefortovo detention facility.
And, there are now rumblings that Paul Whelan, who has American and British citizenship, may be used by Russia as a bargaining chip.
Reuters' Christian Lowe in Moscow: SOUNDBITE (English) RUSSIA BUREAU CHIEF CHRISTIAN LOWE, SAYING: "Since Whelan's detention there has been some talk that potentially there could be some kind of swap in the offing.
Whelan could be exchanged for Maria Butina, that's a Russian citizen who is being detained in the United States.
She admitted in a U.S court that she was working as an agent for Moscow trying to influence and infiltrate American Conservative groups.
That possibility of a swap has been raised, by among other people, a former CIA station chief in Moscow." Whelan's arrest last month has prompted calls from Western powers for answers.
British Foreign Secretary Jeremy Hunt is one of them.
(SOUNDBITE) (English) BRITISH SECRETARY, JEREMY HUNT, SAYING: "We need to see what these charges are against him, understand whether there is a case or not.
We are giving every support that we can.
But we don't agree with individuals being used in diplomatic chess games." On Wednesday (June 3), U.S. Secretary of State Mike Pompeo said that the U.S. will demand Whelan's immediate return if it determines his detention is inappropriate.
Whelan's family say he's innocent -- that he was in Russia attending the wedding of a friend from the Marine Corps.
Whelan's arrest brings an end to an informal truce where Russia had publicly agreed not to aggressively chase U.S. counter intelligence activities over the past two years.