“The fate of a criminal case against two former J.P. Morgan Chase & Co. traders accused of hiding losses rests on what the ‘London whale’ trades were actually worth.

“A key defense for Javier Martin-Artajo and Julien Grout, the two traders targeted in charges announced Wednesday by U.S. prosecutors, is expected to be that the high-stakes derivatives bets their unit made were difficult to value, according to people close to the two.

“Messrs. Martin-Artajo and Grout also have to weigh whether to travel to the U.S. to face the charges, try to strike a plea deal with the government or remain for now in places from where they can’t easily be extradited.

“The situation presents tricky questions for prosecutors who must decide whether they should move more aggressively to bring the defendants to the U.S. or wait for their next move. One option being considered by the Federal Bureau of Investigation and prosecutors is working with local authorities on extradition proceedings where possible. The prospects of extraditing from Spain are better than France, said people close to the case.”

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