J.P. Morgan Chase & Co. ignored or dismissed warning signs about the Madoff fraud even as it earned hundreds of millions of dollars from its relationship with his firm, according to a lawsuit unsealed Thursday.

The $6.4 billion lawsuit, filed in federal bankruptcy court, claims that bankers at J.P. Morgan discussed the possibility that Bernard Madoff was operating a Ponzi scheme, worried that a firm of such size was audited by a storefront accountant and called his returns "too good to be true."

"While numerous financial institutions enabled Madoff's fraud, JPMC was at the very center of that fraud, and thoroughly complicit in it," according to the 115-page lawsuit, filed under seal in December by Irving Picard, the trustee seeking to recover money for Mr. Madoff's victims and made public on Thursday.

The complaint seeks the return of nearly $1 billion in J.P. Morgan's profits and fees, and $5.4 billion in damages. It goes into great detail about the bank's alleged efforts, starting in about 2006, to make money by offering products tied to Mr. Madoff through investment funds that fed money to him.