The founding director of the Association for Research into Crimes against Art estimates that about 75 percent of art crimes involves antiquities. The high rate of antiquities is due to the retail sale value. A stolen painting is only able to get about 10 percent of its auction value due to its high-profile nature and the well-documented ownership trail. Antiquities, on the other hand, are able to fetch its full price on the market by forging its history and ownership.
Source: Ian Johnston, “New ‘intelligence’ body set to fight illicit trade in world’s priceless treasures,” NBC News, November 14, 2012.