Two former JPMorgan Chase & Co. employees were charged with conspiracy for trying to conceal the size of the investment bank’s $6 billion trading loss last year, authorities said in court papers unsealed Wednesday.

Javier Martin-Artajo, Julien Grout and their co-conspirators were accused of “artificially increasing the market value of securities to hide the true extent of hundreds of millions of dollars of losses,” according to court papers.

Martin-Artajo, who supervised JPMorgan’s trading strategy in London, and Grout, who recorded the value of the bad investments, are accused of wrongdoing related to a surprise loss by a trader who has become known as the “London Whale,” a name referring to the trader’s location and to the supersized bets that he made. The two are accused of conspiring to hide more than a half-billion dollars of losses in a credit derivatives trading portfolio that ultimately lost over $6 billion.

JPMorgan spokesman Joe Evangelisti declined to comment.

Martin-Artajo and Grout were charged in criminal complaints in U.S. District Court in Manhattan with conspiracy to falsify books and records, commit wire fraud and falsify Securities and Exchange Commission filings.

In July 2012, JPMorgan announced it would restate its first quarter results for net revenue by $660 million. According to the court papers, the fraud was carried out from at least March 2012 through May 2012.

Prosecutors announced Wednesday that they had entered a non-prosecution agreement with the trader who allegedly made the bad bets, Bruno Iksil. The agreement dated June 20 says Iksil won’t be prosecuted for any crimes, excluding criminal tax violations that may stem from his descriptions of what happened.

According to the court papers, no testimony or other information given by him or any other information prosecutors have gained through his efforts will be used against him in any criminal tax prosecution. The deal requires him to cooperate fully with prosecutors, the FBI and any other law enforcement agency designated by the government.

The bank has acknowledged mistakes but has been adamant that it did not try to mislead investors. Authorities have since questioned whether the bank tried to cover up the loss or downplay it to investors and regulators.

The trading loss in 2012 raised fresh questions as to whether Wall Street banks had learned their lessons from the financial crisis of 2008.

Federal prosecutors planned a news conference to discuss the case.

(AP)