U.S. Attorney for the District of Columbia Ronald Machen will step down April 1, he announced Monday.
Machen, 45, has been in office five years, with the longest tenure for a top federal prosecutor in Washington in nearly four decades, but his investigation into an illegal shadow campaign that helped elect former D.C. Mayor Vincent Gray in 2010 is incomplete and continuing.
Half a dozen people, including Gray's 2010 campaign driver, have pleaded guilty to felonies as a result of Machen's investigation into the shadow campaign. Gray has maintained his innocence.
Machen's principal assistant, Vincent "Vinnie" Cohen Jr., will become acting U.S. attorney after Machen steps down.
"Ron Machen has distinguished himself as a skilled leader, a devoted public servant, and a forceful champion of justice on behalf of the American people," Attorney General Eric Holder, one of Machen's predecessors in the job, said in a statement. "I know firsthand the unique demands of leading the nation's largest U.S. Attorney's office. But Ron has never been deterred by a difficult challenge, nor slowed in his pursuit of a safer, stronger Washington."
A year ago, a prosecutor in Machen's office said in court that Gray knew about and participated in a scheme to illegally fund his campaign. Gray, a Democrat, lost his bid for re-election about three weeks after that revelation from Machen's office.
The investigation of a businessman who admitted to setting up a slush fund to aid Gray's campaign also revealed that the businessman and his associates had done similar work for Hillary Rodham Clinton in 2008, albeit on a much smaller scale.
Machen's office also secured convictions against the then-chairman of the D.C. Council and two council members.
Also ongoing is the prosecution of Ahmed Abu Khattalah, who's alleged to have taken part in the 2012 terrorist attacks that killed four Americans in Benghazi, Libya. Under Machen, the office has secured 13 convictions in terrorism-related cases.
"Serving as the U.S. Attorney for the District of Columbia has been the highest honor of my professional career," Machen said in a statement. "I leave this position confident that my extraordinary colleagues will continue to pursue justice and protect the residents of the District and this great nation."
On Monday, D.C. Mayor Muriel Bowser praised Machen's service to the city, and assured the public that the city has moved beyond the continuing scandal investigation.