Who Killed KGB Agent Alexander Litvinenko?

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A visitor looks at a painting showing former Russian spy Alexander Litvinenko, by Dmitry Vrubel and Viktoria Timofeyeva painters in the Marat Guelman gallery in Moscow, 23 May 2007.
( NATALIA KOLESNIKOVA/AFP / Getty )
Produced by Mythili Rao
PRI WNYC