There is for example a brief discussion of one of these figures:
For its information about antiquities trafficking, the report relies almost exclusively on reports from major media outlets such as the New York Times, Guardian, Wall Street Journal, and Washington Post. Unfortunately major media outlets have frequently been the purveyors of inaccurate information on this topic, and this has negatively impacted the report. The report correctly identifies Lebanon, Turkey and Jordan as major transshipment points for antiquities smuggling. However, experts on the Syrian antiquities trade generally believe that much looted material either moves east rather than through closely monitored auction houses in London and New York, or that it is kept within the region in hopes of selling it in a few years when suspicions die down. When it comes to estimating the value of antiquities looting to ISIS the report relies on outdated information, misrepresented statistics, and discredited figures.
The often-repeated $36 million figure comes from Martin Chulov’s reporting in The Guardian. The figure has been widely questioned on this site and elsewhere. Chulov took his figure from captured documents shown to him by an Iraqi intelligence officer. It appears to show income from looting or ghanima, which in ISIS’ terminology means the expropriation of money and property from local populations. Looting of archaeological sites is classified as the extraction of al-rikaz or a “natural resources from the earth” akin to oil, gas, minerals and precious metals. Profits from digging are taxed at a 2o% to 50% rate, unlike ghanima which is expropriated wholesale.Jones adds: 'My own research based on available open source data concurs with this figure, estimating that ISIS has made a few million dollars from antiquities and that taxing looters accounts for less than one percent of the organization’s budget' before noting:
Unfortunately, the congressional staffers who wrote this report seem to have simply searched for reports published in major media outlets without critically examining them. Much of the media coverage of archaeological looting in Iraq and Syria has been drive by sensationalism. With reports like this there is a very serious danger that sensationalized articles and bogus figures could drive policy recommendations with regards to prosecuting the war against ISIS.