What caused the 'flash crash', man or machine?

One challenge market regulators are up against is the rapid rise of the ultra-fast, high frequency trader. One man who held that job description was Navinder Singh Sarao. He's the 36 year old British man accused of helping to trigger Wall Street's "Flash Crash" in 2010. On Wednesday he appeared before a London court, where he was told he'll be kept in custody after failing to raise the seven and a half million dollar bail money needed to secure his release. He's fighting attempts to extradite him from Britain to the US, after he was charged with a number of counts of fraud by the US Department of Justice. Mr Sarao denies the charges. His case has attracted attention around the world as, according to some, it highlights weaknesses in the way markets work and are regulated. Our business correspondent, Theo Leggett, reports: