It may be a touchy subject to some, but I feel the violinist, Mr. Fenrych, is the rightful owner. Mrs. Moore suspected it authenticity, obviously, but still chose to freely sell the item. If she had a contract written about the "what ifs", then by all means I believe she has a valid claim, if not, she is out and probably for the better. A person who did want it regardless of the circumstances and paid a nice agreed upon  price to obtain it.