A court-appointed examiner investigating Lehman Brothers Holdings Inc.'s bankruptcy has been exploring whether the Federal Reserve improperly cut in front of other creditors owed money in the $613 billion bankruptcy case, records show.

Billing records filed with the court show the examiner is investigating an issue that has angered many of Lehman's creditors: how the Federal Reserve and the New York Fed -- which lent Lehman $46 billion in cash and securities before its bankruptcy filing last September -- were paid promptly and in full, while tens of billions of dollars in other debts were left to be sorted out in court. It remains unclear when and how much Lehman creditors will be repaid.

The examiner, Anton Valukas, chairman of law firm Jenner & Block LLP and a former U.S. attorney, said, "I am under a court order not to discuss what we are doing or how we are doing it."

Fed loans were crucial to propping up Lehman during its final days, and were part of an extraordinary government attempt to stabilize Lehman in the chaotic weeks of mid-September 2008. The government ultimately quashed a rescue of Lehman, which filed for bankruptcy protection. But its earlier steps now are open to scrutiny in bankruptcy court.

Details on the examiner's work remain scant, and it is possible no actions will be brought. Should the examiner determine that the Fed got preferential treatment, bankruptcy administrators could pursue court claims to recover assets for Lehman's creditors from the Fed, on the theory those assets should have remained with Lehman when it filed for bankruptcy last September.