IT IS BECOMING MORE and more difficult to believe that alleged wrongdoing in D.C. Mayor Vincent C. Gray’s 2010 election campaign was limited to ill-advised dealings with a fringe mayoral candidate. Evidence of a “shadow campaign” that operated outside the rules raises new issues for Mr. Gray (D): If he knew of such an operation, he was complicit; if he was clueless, he was negligent. Either way, the public is owed a better explanation than the no-comment that was the mayor’s muted ­response to these latest allegations.

A federal investigation into Mr. Gray’s election — prompted by allegations last year from Sulaimon Brown that he received money and the promise of a city job for his campaign attacks on then-Mayor Adrian M. Fenty (D) — has taken on new, more serious, dimensions. The Post’s Nikita Stewart reported Thursday that federal investigators are examining a get-out-the-vote effort on Mr. Gray’s behalf that involved contributions and expenditures not reported as required by campaign finance laws.

Not only did The Post uncover examples of campaign activity that went unreported but also it showed links to the funding network of businessman Jeffrey E. Thompson that has also come under federal scrutiny. Equally troubling is the revelation that the operation was run by Vernon E. Hawkins, a fixture in D.C. politics who is a longtime ally and friend to Mr. Gray, who sometimes operated out of the campaign’s downtown headquarters. “It’s increasingly clear that there was a shadow campaign that the legitimate campaign didn’t know anything about,” was the devastating conclusion of Mo Elleithee, the political consultant who handled communications for the Gray campaign.

Mr. Gray declined to comment on The Post’s report, citing the ongoing investigation. Previously, in the aftermath of federal raids on the home and offices of Mr. Thompson, the mayor said, “So as I look back at my own involvement, it was a lot of activity, and we did it with the utmost integrity.” We continue to hope that is true. But each new revelation — like the report by WRC-TV’s Tom Sherwood that Mr. Gray personally collected as much as $100,000 from Mr. Thompson and his associates — raises the importance of hearing a more substantive explanation from the mayor.