 next if the airstrikes continued. On 2 September 2014, ISIS released a video purportedly showing their beheading of Sotloff. In the video the executioner says, "I'm back, Obama, and I'm back because of your arrogant foreign policy towards the Islamic State, because of your insistence on continuing your bombings and on Mosul Dam, despite our serious warnings. So just as your missiles continue to strike our people, our knife will continue to strike the necks of your people."  The next scene shows the same executioner holding the orange jumpsuit of another prisoner, and saying "We take this opportunity to warn those governments that enter this evil alliance of America against the Islamic State to back off and leave our people alone." On 13 September 2014, ISIS released another similar video purportedly depicting the beheading of David C. Haines, a British aid worker they had been holding hostage.
There are many foreign fighters in ISIS's ranks. In June 2014, The Economist reported that "ISIS may have up to 6,000 fighters in Iraq and 3,000–5,000 in Syria, including perhaps 3,000 foreigners; nearly a thousand are reported to hail from Chechnya and perhaps 500 or so more from France, Britain and elsewhere in Europe". Chechen leader Abu Omar al-Shishani, for example, was made commander of the northern sector of ISIS in Syria in 2013. According to The New York Times, in September 2014 there were more than 2,000 Europeans and 100 Americans among ISIS's foreign fighters.
A study of 200 documents—personal letters, expense reports and membership rosters—captured from Al-Qaeda in Iraq and the Islamic State of Iraq was carried out by the RAND Corporation in 2014. It found that from 2005 until 2010, outside donations amounted to only 5% of the group’s operating budgets, with the rest being raised within Iraq. In the time-period studied, cells were required to send up to 20% of the income generated from kidnapping, extortion rackets and other activities to the next level of the group's leadership. Higher-ranking commanders would then redistribute the funds to provincial or local cells that were in difficulties or needed money to conduct attacks. The records show that the Islamic State of Iraq was dependent on members from Mosul for cash, which the leadership used to provide additional funds to struggling militants in Diyala, Salahuddin and Baghdad.
In mid-2014, Iraqi intelligence extracted information from an ISIS operative which revealed that the organization had assets worth US$2 billion, making it the richest jihadist group in the world. About three quarters of this sum is said to be represented by assets seized after the group captured Mosul in June 2014; this includes possibly up to US$429 million looted from Mosul's central bank, along with additional millions and a large quantity of gold bullion stolen from a number of other banks in Mosul. However, doubt was later cast on whether ISIS was able to retrieve anywhere near that sum from the central bank, and even on whether the bank robberies had actually occurred.
ISIS has routinely practised extortion, by demanding money from truck drivers and threatening to blow up businesses, for example. Robbing banks and gold shops has been another source of income. The group is widely reported as receiving funding from private donors in the Gulf states, and both Iran and Iraqi Prime Minister Nouri al-Maliki have accused Saudi Arabia and Qatar of funding ISIS, although there is reportedly no evidence that this is the case.
The group is also believed to receive considerable funds from its operations in Eastern Syria, where it has commandeered oilfields and engages in smuggling out raw materials and archaeological artifacts. ISIS also generates revenue from producing crude oil and selling electric power in northern Syria. Some of this electricity is reportedly sold back to the Syrian government.
Since 2012, ISIS has produced annual reports giving numerical information on its operations, somewhat in the style of corporate reports, seemingly in a bid to encourage potential donors.
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