New York state's top financial regulator has demanded documents from more than a dozen banks including Barclays, Deutsche, Goldman Sachs and RBS as a probe widened into trading practices in the $5.3tn-a-day global foreign exchange markets. Benjamin Lawsky, New York's financial services superintendent, made the move following the banks' decision to fire or suspend at least 20 traders following reports that employees at some firms had shared information about their currency positions with counterparts at other companies. Lawsky's move marks the latest escalation in a global investigation by regulators into the manipulation of benchmark rates. The currency probe comes as regulators are still investigating the manipulation of the Libor lending rate by traders at some of the world's biggest banks. The Wall Street Journal reported that Goldman Sachs' Steven Cho, formerly global head of spot and forward foreign exchange trading for major currencies, was retiring from the bank. His departure came a day after Citigroup announced that Anil Prasad, its global head of foreign exchange, was leaving the company. It is not know if his retirement is in any way linked to any investigation. Prasad's exit comes a month after Rohan Ramchandani, formerly Citi's head of European spot foreign exchange trading, was fired. Ramchandani had been a member of the Bank of England's foreign exchange joint standing committee.