Many Gray supporters view Machen's office with suspicion and said it was unfair for prosecutors to accuse the mayor of wrongdoing without charging him with a crime. Polls showed Gray with a comfortable lead before the latest developments in the investigation.
"He cannot convince a jury that Vince Gray is guilty," said Chuck Thies, Gray's campaign manager. "Instead, Ron Machen used propaganda to try Vince Gray in the court of public opinion in the closing weeks of this election."
Bowser, 41, worked for the local government in suburban Montgomery County, Md., and served as an elected neighborhood commissioner in the district before election to the council in 2007.
Opponents said Bowser lacks experience to be mayor, saying her legislative record is skimpy. Her most significant accomplishment on the council was the creation of an independent ethics board able to punish officials for violations. The board has found wrongdoing by three members of the 13-person council.
Gray, 71, led nonprofit organizations and the city's Department of Human Services before he was elected to the D.C. Council in 2004. As mayor, he's been known as a pragmatic, detail-oriented technocrat and sound manager of the city's robust finances. The district has enjoyed a surging population, a booming real estate market and relatively low violent crime.