'Femme fatale'

Also known as Anya Kushchenko, the 28-year-old was arrested on June 27 in Manhattan, New York, where she ran a $2m property business, her lawyer said in court last week.

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Alex Chapman, her former husband, spoke earlier this month about how his wife's personality changed dramatically in the final stages of their marriage.

He told Britain's Daily Telegraph newspaper that Chapman, underwent a "dramatic change in the way she thought and went about things" after falling in with a group of Russian friends.

"It was like someone having a midlife crisis, but in their 20s. She would arrange to go out, but when I said I would join her, she told me not to bother because they would all be speaking Russian," he told the paper.

Chapman, who held Russian-UK nationality, soon became the focus of a worldwide media frenzy, with the press describing her as a "femme fatale".

Michael Farbiarz, an assistant US attorney, said that behind the facade she was a "sophisticated agent of Russia".

Ten people, including Chapman, who admitted being agents for Russia were exchanged in Vienna on Friday for four individuals imprisoned in Russia for their contacts with Western intelligence agencies.