Here's an interesting idea, although it may be far fetched. Given the original, if a thief could produce a high quality counterfeit in van gough's style, they could possibly use parchment/ink from the true original in creating it. Then they'd have a "lost van gough" which could pass some basic age analysis. This lost painting would be worth more than the original, and they could sell it on the real art market, not a black market.

Or this may just a crappy movie plot. I don't know much about art.