I just had a small problem with the identity theft that he does, couldn't it be easily found out in today Google age? Plus the police assuming that he's dead without a body so easily was also a bit unbelievable!!!!!!!!
He went to the passport office claiming he lost his passport. Since he had the passport number he was able to get a new passport, one with his own picture rather than the dead guy's picture.
One of the reasons he fled after the gallery showing was because he was going to have to do interviews in London, which he couldn't do. He had also negotiated with the Yugoslavian woman not to have his picture taken.
I guess no one knew what the dead guy looked like when they Googled him because he was never really famous, although it's strange that his photography work was available online but not a picture of himself.
After he was told about the London interviews they'd set up, they mentioned that the Parisian interviewer knew him (the real Gregoire) - that's when he told Ivana he needed air and had to get out of the gallery. For a guy on the run looking for a quiet life, it was surprising that he chose a high profile way of earning a living. I enjoyed this movie. There were a few little things such as his disappearance and his victim's disappearance that could have been dealt with in more detail.
You might want to read the book by Douglas Kennedy published in 1997. The original story is all set in the USA with the husband being an (economically) very successful Wall Street Lawyer (Jr. Partner in a mid-sized firm before age 40).
Evidently (per Amazon reviews, etc.) this American author is more popular in Europe than here which is why the movie was made in France and "transitioned" to Europe and in 2010. It's an odd mixture of what has been technologically updated and what hasn't been from late 1990's to the 21st century. The thing the husband was able to do most successfully was learn to copy G's signature - the trick being "copy it upside down" - and just use "snail mail" for most everything. In the book he had Gary's (Gregoire in the movie) checkbook and trust documentation - so he basically lived off G's periodic trust fund monies - until he started making some money from his photography. In the book his ex-wife and her new "ex-Wall Street rich guy art gallery owner" actually came to his gallery opening in small-town Montana and THAT is when he really panicked and fled just before she spotted him. As almost always, I liked the book better.
But I would have rewritten at least the ending this way: In the book he left his wife almost 1.5 million dollars in life insurance and savings PLUS the house and all her original antique expensive furniture - so when she showed up at his gallery I would have whispered in her ear "you need to keep your mouth shut and listen to me - unless you WANT to give that $million dollars back to the insurance folks?" I would have then extorted a mere $100k from her for some small plastic surgery changes to look more like G - maybe just some added scarring as well and claimed a "really bad auto accident". He could THEN have enjoyed his new artistically successful life. ;-)