The U.S. government admitted liability in an air collision in the skies above the nation's capital that killed 67 people early this year, opening the door for the families of victims to seek damages for the crash, according to court documents. In a 209-page document filed in a federal lawsuit brought by the family of one of the victims , the Justice Department said that the Army pilots flying a Black Hawk helicopter the night of Jan. 29 had failed to maintain "vigilance" and "proper and safe visual separation" with a commercial airliner before it crashed into the jet over the Potomac River.