Ambac said it has incurred more than $200 million of claims on seven residential mortgage-backed securities transactions dating from 2006 that Bear fraudulently induced it to enter, and which collectively have lost $1.83 billion.
It said the transactions "have failed miserably," with the rate of default or severe delinquency on the underlying loans ranging from 41.4 percent to 61.7 percent.
"Driven by management's 'Bear don't care' mentality, Bear Stearns perpetrated a massive fraud that deceived investors and financial guarantors, such as Ambac, into believing that the mortgage loans backing its securitizations were originated pursuant to established underwriting guidelines and were therefore of good quality," Ambac said.
JPMorgan did not immediately return a call seeking a comment.
The lawsuit is the second filed by Ambac in the New York State Supreme Court to arise from activities at Bear and its EMC Mortgage unit.
Assured Guaranty Ltd, a bond insurer backed by the billionaire Wilbur Ross, has filed a similar lawsuit against the largest U.S. bank.
JPMorgan bought Bear in May 2008 in a buyout brokered by the U.S. Federal Reserve. Both are among the many large banks accused in lawsuits or by regulators of misconduct in the creation and marketing of mortgage-backed securities.
On Feb. 29, JPMorgan said U.S. Securities and Exchange Commission staff was mulling civil charges or administrative proceedings in two mortgage probes.
It said one probe involved due diligence and disclosures for two mortgage-backed securitizations, and the other involved loans used in mortgage securities created by Bear.
Ambac on March 14 won court approval to emerge from Chapter 11, which it entered in November 2010.
Once the second-largest U.S. bond insurer, Ambac sought protection from creditors after straying from its main business of insuring municipal bonds, and suffering large losses from guaranteeing bonds backed by risky mortgages.
The case is Ambac Assurance Corp et al v. EMC Mortgage LLC et al, New York State Supreme Court, New York County. (Reporting By Jonathan Stempel and Karen Freifeld in New York; Editing by Gerald E. McCormick and Maureen Bavdek)
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