Navinder Singh Sarao, 36, was arrested in London on Tuesday, charged with market manipulation and wire fraud. The CME Group, the platform Sarao used for his trades and also a self-regulatory organization, first started talking to him about his trades in 2009, but he continued his alleged manipulation well into this year. “This will raise concerns about the stability of financial markets,” said Robert Engle, finance professor at New York University’s Stern School of Business.