Lehman Brothers Holdings Inc and its unsecured creditors asked a bankruptcy judge on Thursday to unseal court documents related to an investigation of the sale of Lehman's core U.S. assets to Barclays PLC .

Earlier this month, Lehman asked a judge to revisit the sale of Lehman's brokerage to Barclays Capital claiming that the British bank got an improper $8.2 billion windfall profit from excess assets it took control of in the September 2008 deal. About 50 pages of the request were redacted and not made public due to certain confidentiality agreements.

In court papers filed on Thursday, Lehman's official committee of unsecured creditors asked Judge James Peck if the court could unseal most of the document, as well as certain exhibits.

The Court authorized an investigation to illuminate the facts and circumstances surrounding the Sale Transaction. The inability to disclose the results of that investigation offends the spirit and purpose of the Court's instruction, Lehman's creditors wrote in the request.

Lehman Brothers and the trustee charged with liquidating Lehman's brokerage unit filed additional court papers supporting the creditors' request to unseal the documents.

Lehman received approval in June to probe whether Barclays got too good of a deal when it bought Lehman's brokerage business, as the British bank was able to quickly book a $4.2 billion gain on its $1.75 billion purchase.

Barclays has said Lehman is making an opportunistic claim and trying to re-trade the deal now that the economy has stabilized.

A court hearing on the topic is set for October 15, according to court papers.

The case is In re: Lehman Brothers Holdings Inc, U.S. Bankruptcy Court, Southern District of New York, No. 08-13555.

(Reporting by Emily Chasan; Editing by Marguerita Choy)