Two former JPMorgan Chase & Co. traders were charged Wednesday over last year\'s \"London Whale\" scandal, which cost the bank 6.2 billion dollars, Federal prosecutors said Wednesday. However, Bruno Iksil, a third trader who became known as the \"London Whale\" for the size of the derivatives trades he made, was not charged after gaining immunity in exchange for helping with the investigation. Javier Martin-Artajo, a supervisor at JPMorgan\'s chief investment office in London, and subordinate Julien Grout were charged with the criminal offences of conspiracy to falsify books and notes, commit wire fraud and falsify Securities and Exchange Commission (SEC) filings, allegedly to hide the fact that an investment portfolio was plummeting in value. They were also charged separately in an SEC civil complaint. U.S. Attorney Preet Bharara hinted the misconduct was not just the work of a couple of rogue traders, but was systemic in a bank that failed to keep adequate watch over its traders. He said companies needed to pay closer attention to the cultures they created. The charges focus on an investment portfolio whose components were supposed to be marked at their market value each day as best as the bankers could approximate. The SEC alleges that, from March to May 2012, at Martin-Artajo\'s direction, Grout began using prices for the portfolio \"deliberately chosen to minimize losses rather than represent fair value.\" The so-called \"London Whale\" trades were a complex set of synthetic credit derivatives trades conducted in the bank\'s London office in early 2012 and ended up costing the bank at least 6.2 billion dollars, according to a 301-page report by the Senate\'s Permanent Subcommittee on Investigations.