ANY DOUBT about the seriousness of the investigation into D.C. Mayor Vincent C. Gray’s 2010 election campaign was ­removed Monday, when a federal prosecutor filed criminal charges stemming from the year-long inquiry.

The charges bolster the credibility of fringe mayoral candidate Sulaimon Brown and allegations about the Gray campaign. They also implicate a longtime member of Mr. Gray’s inner circle. And the decision by U.S. Attorney Ronald C. Machen Jr. to bring felony obstruction of justice charges shows a determination to get to the bottom of these troubling matters.

Thomas W. Gore, Mr. Gray’s assistant campaign treasurer, is charged in a federal information — a filing that typically means a defendant has agreed to plead guilty — with violating the District’s campaign finance laws by making straw political donations and then destroying evidence related to those contributions to hinder the federal investigation. A hearing has been set for Tuesday before U.S. District Judge Colleen Kollar-Kotelly.

Mr. Gore’s attorney, Frederick Cooke, did not dispute that a guilty plea is likely. If convicted, Mr. Gore faces up to 20 years on the obstruction of justice charge, while each misdemeanor campaign finance charge carries a maximum sentence of six months and fines.

In their filing, prosecutors allege that Mr. Gore destroyed a spiral notebook containing information about $535 in money orders that used the names of other people to shield their source. The recipient of the largess is not named in Monday’s filing, but records made public earlier show that Mr. Brown, a minor candidate in the 2010 Democratic primary, was the recipient.

Mr. Brown has said that the Gray campaign gave him money and promised him a city government job in exchange for his relentless campaign attacks on former Mayor Adrian M. Fenty, who was Mr. Gray’s chief rival. Federal prosecutors allege that Mr. Gore destroyed this incriminating notebook “on or about March 6, 2011.” That is the day Mr. Brown’s charges were first reported by the Post’s Nikita Stewart.

Mr. Gray has denied any wrongdoing. On Monday his office directed inquiries to his personal attorney, Bob Bennett, who refused to comment. Mr. Bennett may be looking out for the best interests of his client by not commenting on an active and apparently deepening investigation, but District residents are right to wonder why Mr. Gray — if he has nothing to hide, as he contends — isn’t expressing shock or disappointment or anger.

Mr. Gore managed Mr. Gray’s finances when he ran for the Ward 7 seat on the D.C. Council and again when he ran for council chairman. How did it come about that he allegedly directed these bogus money orders to Mr. Brown? What were the circumstances that allegedly prompted him to destroy records? Were others consulted?

Mr. Cooke said that his client has been answering prosecutors’ questions but declined to predict whether prosecutors would characterize Mr. Gore as cooperating. City residents have to hope that Monday’s action means the troubling uncertainty that has shadowed Mr. Gray and his administration is finally on its way to being resolved, one way or another.