Morgan Stanley successfully pushed Standard & Poor's and Moody's Investors Service Inc. to give unwarranted investment-grade ratings in 2006 to $23 billion worth of notes backed by subprime mortgages, investors claimed in a lawsuit, citing documents unsealed in federal court.

Executives at the ratings firms failed to warn investors about the risks associated with subprime-backed notes that were issued by a unit of London-based hedge fund Cheyne Capital Management Ltd. because they wanted to reap financial rewards from doing business with Morgan Stanley, the sixth-largest U.S. bank by assets and designer of the notes, the investors allege, citing the material made public yesterday in Manhattan.

The unsealing of the internal documents from Moody's and Standard & Poor's came in one of the largest ratings lawsuits to emerge from the 2008 financial crisis. The lawsuit was filed in 2008 by Abu Dhabi Commercial Bank, based in the United Arab Emirates, and Washington's King County, which includes Seattle.