Prices for Russian art, books, manuscripts and historical memorabilia have risen rapidly since 2000, and this has been accompanied by an increase in thefts from Russian museums and archives. In August 2006, the Hermitage disclosed that 226 Russian works of art had been stolen by staff over the previous decade.
Will any charges ensue? Someone made up a provenance for these objects somewhere between their theft in Moscow and consignment to Christie's. I'd imagine it wasn't the final consignor though, these letters probably passed through a few hands first, and were "laundered". Perhaps not enough to justify their sale, but probably enough to preclude criminal charges or an investigation.