U.S. investigators uncovered a global financial network run by a senior Islamic State official that funneled money to an alleged ISIS operative in the U.S. through fake eBay transactions, according to a recently unsealed FBI affidavit.

The alleged recipient of the funds was an American citizen in his early 30s who had been arrested more than a year ago in Maryland after a lengthy Federal Bureau of Investigation surveillance operation that found the first clues to the suspected network.

The government had alleged in a 2016 indictment that the American suspect, Mohamed Elshinawy, pledged allegiance to Islamic State and had pretended to sell computer printers on eBay as a cover to channel payments for Islamic State through PayPal, potentially to fund terror attacks.

The recently unsealed FBI affidavit, filed in federal court in Baltimore, alleges that Mr. Elshinawy was part of a global network stretching from Britain to Bangladesh that used similar schemes to fund Islamic State and was directed by a now-dead senior ISIS figure in Syria, Siful Sujan.

The U.S. has said Mr. Elshinawy told investigators he was instructed to use the money for “operational purposes” in the U.S., such as a possible terror attack. He has pleaded not guilty to supporting the terror group, and currently is in federal custody awaiting trial. His lawyer declined to comment.

The case suggests how Islamic State is trying to exploit holes in the vast online financial world to finance terror outside its borders.

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