NEW YORK – JPMorgan Chase, the bank where Bernard Madoff kept his clients’ money, said in a court filing Tuesday that it had no legal obligation to figure out that the Ponzi king’s investment scheme was a fraud.

The bank is defending itself against a $6.4 billion lawsuit by the court-appointed trustee trying to restore all of the money Madoff stole to its rightful owners. In the suit, Irving Picard claimed the bank had suspected for years that something was amiss with Madoff’s operation. He cited internal e-mails and documents in which bank officials expressed concerns about the secretive nature of Madoff’s office, and a disconnect between his stellar profit margins and the market’s performance.

JPMorgan said that Picard was trying to get the courts to create new law holding banks to much tougher accountability standards and also challenged Picard’s right to bring the case.