Few things are ordinary about Bernard Madoff’s alleged $50bn fraud – including the way it is being ­investigated.

Manhattan mystery: the SEC, the US Attorney’s office and the FBI are all investigating the Madoff case

The Securities and Exchange Commission, the main US financial markets watchdog, is conducting the civil investigation into the alleged $50bn “Ponzi” scheme, which came to light after Mr Madoff’s sons turned him in last month.