NEW YORK: A Lehman Brothers whistleblower warned his bosses that accounting gimmicks the bank used before its collapse may have been illegal, his lawyer said Friday.

Matthew Lee, a former Lehman senior vice president, was fired days after questioning the accounting tricks in a letter to his superiors, attorney Erwin Shustak said. Shustak gave a copy of the letter to The Associated Press.

Lehman Brothers Holdings Inc. imploded in September 2008, becoming the biggest corporate bankruptcy in U.S. history. The collapse sent financial markets across the globe into a free-fall and prompted a massive bailout of the U.S. banking system.

An examiner appointed by the bankruptcy court said in a 2,200-page report last week that Lehman hid its debt and perilous financial condition by using an accounting gimmick called Repo 105. The report revealed Lee's warnings to the bank, though his letter makes public the first internal assessment of the legality of Lehman's bookkeeping.

In a letter dated May 18, 2008, Lee wrote that he discovered that the bank had been underreporting its debt by about $5 billion at the end of each month. Lee, a 14-year Lehman veteran, wrote that he felt compelled to report the "discrepancies" under the firm's code of ethics, saying he believed they "possibly constitute unethical or unlawful conduct."

"I believe the manner in which the firm is reporting these assets is potentially misleading to the public and various governmental agencies," Lee wrote. "If so, I believe the firm may be in violation of the code."

Days after sending the letter, the firm told Lee he was being terminated as part of a general layoff, Shustak said. After his firing, Shustak wrote a letter to the bank saying that Lee "believes he has been the victim of retaliation for bringing what he believed, in good faith, to have been ethical and securities law violations by Lehman."

Lee, 56, later reached a severance agreement with Lehman, however, he stopped receiving payments after the firm's collapse, Shustak said. He has filed a claim with the bankruptcy court to recover the unpaid amount.

The bankruptcy examiner's report and Lee's letter could provide a framework for any future legal action against Lehman executives.

Senate Banking Committee Chairman Christopher Dodd on Friday called for Attorney General Eric Holder to investigate the circumstances that led to Lehman's collapse. A Justice Department spokeswoman said the department would review the request.

The examiner, Anton Valukas, discovered that Lehman put together complex transactions that allowed the firm to sell "toxic," mostly mortgage-backed, securities at the end of a quarter — wiping them off its balance sheet when regulators and shareholders were examining it — and then quickly buy them back.

His report doesn't conclude whether executives violated securities laws. It does say that the executives' decision not to disclose the effects of its business judgments appears to be sufficient evidence to support the awarding of civil damages in a trial.

The executives named by the report include former CEO Richard Fuld and three chief financial officers. Fuld has denied knowing what the transactions were or the accounting for them.

Securities and Exchange Commission Chairman Mary Schapiro said Wednesday that the agency is investigating several companies' actions in the run-up to the financial crisis of 2008. She said the SEC's review of the Lehman disaster "has taken us down a path where we're looking broadly" and that Valukas's report will be helpful to the agency in its investigation. She did not name other firms.