It was last November, and Mr. Weinstein, a wunderkind of the New York hedge fund world, had spied something strange across the Atlantic. In an obscure corner of the financial markets, prices seemed out of whack. It didn’t make sense.
It might seem remarkable that someone like Mr. Weinstein, a man virtually unknown outside of financial circles, could deal such a stinging blow to one of the world’s largest, most respected banks. Jamie Dimon, the chairman and chief executive of JPMorgan and a face of the banking establishment, is struggling to contain the damage from what he has called a “terrible, egregious mistake.” The loss — JPMorgan put it at $2 billion, but it may turn out to be $3 billion or more — has renewed calls for stronger financial regulation.