Navinder Singh Sarao, the man accused of contributing to the 2010 financial "flash crash", has told a UK court that he did nothing wrong.
Sarao, 36, is facing charges of wire fraud, market manipulation and commodities fraud, over his alleged role in the flash crash of 6 May 2010.
Attending a bail hearing at Westminster Magistrates' Court in London, Sarao stressed his innocence and said he had not "done anything wrong apart from being good at my job. How is that allowed to go on, man?"
Sarao was remanded in custody after a request to reduce bail from £5.05m to £50,000 was refused. His lawyers said he could not raise the funds needed for bail as the US authorities had frozen his assets.
He is scheduled to have a full extradition hearing in August or September after the US Department of Justice accused his company, Nav Sarao Futures, of making £26m illegally over a five-year period.
US authorities have accused Sarao of using an "automated trading programme" to manipulate markets and contribute to the so-called flash crash, when the Dow Jones lost 700 points in a number of minutes, before regaining the lost value in a similar timeframe.
Regulators have pinned the blame for the crash on high-frequency traders making a number of sell orders.