Christie's wouldn't bid stolen goods...
... or at least, they're not supposed to do so. But they mistakenly did.
On June 22, 2006, they performed the auctions to sell nine drawings made by a Ukranian constructivist architect named Yakov Chernikhov (1889-1951), who is recognized as one of the most prominent artists following that movement.
By the time when the auction was expected to take place, Andrej Chernikhov, one of the architect's grandchildren, decided (just by curiosity) to check out in Internet the catalogue of the drawings that were to be sold by Christie's. And what he discovered was really surprising: he had doubts about the authenticity of six of them, which he communicated to Christie's. They decided to proceed with the auction, collecting about 49,000 € for the nine drawings.
But they were forced to cancel such operation, as it was later discovered that such drawings were actually stolen from the Literature and Arts File of Russia. According to the Russian Authorities, those works are various million Euros worth. All of them were returned to Russia.
This is a wicked story, isn't it? The only doubt I have about it is where did Christies obtain that stuff from? Something smells fishy here.