Five years ago, the global financial system was rocked by the “flash crash,” 15 minutes of chaos that shook the world’s biggest markets and prompted investors both big and small to question how such a vital part of the economy could be brought to its knees.

On Tuesday, United States prosecutors said that much of the blame for the event could be pinned on a single person: a 36-year-old man who had been boldly manipulating markets from his suburban rowhouse just a few minutes from Heathrow Airport outside London, where he was arrested.

Regulators said that their prosecution of the trader, Navinder Singh Sarao, demonstrated their aggressiveness in rooting out market manipulation. But news of the arrest, if anything, has raised anew concerns about how an individual could manage to exert such influence over the world’s financial markets. The case also played into worries that have swirled around the increasingly automated and complex financial markets, where regulators have struggled to keep up with nimble new participants like high-frequency trading firms that use sophisticated networks to make money in milliseconds via rapid-fire trades.

For the latest case, it took the authorities five years to track down a rogue actor making enormous trades. And, they were led to him only with the help of an outside whistle-blower.