With the resignation and expected guilty plea of former D.C. Council Chairman Kwame Brown, a team of federal prosecutors looking into political corruption now has an undivided focus on Mayor Vincent Gray, subject of a long-running investigation that recently picked up momentum with the convictions of two Gray associates.

U.S. Attorney Ronald Machen has been probing the Gray campaign for nearly 16 months and last month secured felony guilty pleas from two Gray campaign aides.