Here's the DOJ statement

#08-963: Statement of the Department of Justice’s Antitrust Division on Its Decision to Close Its Investigation of the Merger of Delta Air Lines Inc. and Northwest Airlines Corporation (2008-10-29)

"After a thorough, six-month investigation, during which the Division obtained extensive information from a wide range of market participants –including the companies, other airlines, corporate customers and travel agents –the Division has determined that the proposed merger between Delta and Northwest is likely to produce substantial and credible efficiencies that will benefit U.S. consumers and is not likely to substantially lessen competition." ...