When British trader Navinder Singh Sarao planned to raise money to launch a new investment fund in 2010, he was put in touch with David Cosgrove, an Irishman who had set up dozens of such funds in offshore tax havens.

The NAV Sarao Milking Markets Fund (GBP) was soon registered in Mauritius as part of Cosgrove's financial network. The stuccoed Hounslow, England, home where Sarao traded US and European stock futures became a new outpost in a growing empire of funds overseen by Cosgrove.