THE CAMPAIGN TO elect Vincent C. Gray (D) as D.C. mayor reported total expenditures of $1,293,184.43 in a report filed just days before the 2010 Democratic primary. What was not reported, and not known until Tuesday’s extraordinary proceedings in U.S. District Court, is that another $653,000 — allegedly from a D.C. businessman with significant contractual interests with the city government — was secretly and unlawfully spent to elect Mr. Gray.

Jeanne Clarke Harris’s admission that she conspired with the businessman and others in what a federal judge called a “knowing and conscious flaunting” of campaign laws confirms the existence of a shadow campaign to help Mr. Gray in his successful effort to unseat then-Mayor Adrian M. Fenty. As the federal investigation continues, with more charges expected, it is critical that Mr. Gray address these revelations. His previous claim that he knew nothing of a parallel campaign operation is insufficient in light of the damning details uncovered by federal prosecutors.

Ms. Harris, a public relations consultant, pleaded guilty Tuesday to charges of conspiring to disguise the source of campaign contributions and trying to conceal those activities from investigators by falsifying documents and causing others to destroy records. The scheme to use straw donors to circumvent campaign finance laws dates back a decade and involves a number of federal and local candidates. But it is Ms. Harris’s activities and that of her alleged co-conspirator — reported to be prominent businessman and philanthropist Jeffrey Thompson — in Mr. Gray’s 2010 campaign that was the bulk of the government’s case. Mr. Thompson was not named but is described as “Co-Conspirator No. 1”; he has not been charged, and his lawyer has refused to comment.

Under questioning by U.S. District Judge Colleen Kollar-Kotelly, Ms. Harris acknowledged that she was directed to use thousands of dollars of money funneled by check and wire to her businesses to buy campaign materials — yard signs, banners, lapel stickers and T-shirts that were delivered to Mr. Gray’s campaign offices — and to hire and equip canvassers, coordinators and drivers to support Mr. Gray’s election. She said that the money came from Co-Conspirator No. 1 but the plans for how to spend it came from another person. According to the government’s statement of offense, Ms. Harris and Co-Conspirator No. 1 learned “in or about July 2010” from individuals associated with Mr. Gray’s campaign that financial assistance was needed: “Co-Conspirator No. 1 agreed to fund an effort to support [Mr. Gray’s campaign] with assistance from Harris, which would among other things, identify likely [Gray] voters, encourage those voters to commit to vote for [Mr. Gray] and assist those voters in getting to the polls.” Prosecutors did not allege Mr. Gray knew of the activities but said the effort was “coordinated” with members of his campaign.

Nothing was ever reported because Mr. Thompson allegedly wanted to keep his identity concealed from the public. Mr. Thompson is owner of D.C. Chartered Health Plan and helped found an accounting firm, two businesses that do hundreds of millions of dollars of business with the city. Mr. Gray’s decision early in his administration to provide $32 million to increase reimbursement rates for Mr. Thompson’s firm and another company prompted objections from some council members and raised questions that are far more troubling in light of Tuesday’s revelations.

Ms. Harris is the third person associated with Mr. Gray’s campaign to plead guilty in federal court. It’s pretty apparent she won’t be the last to be charged by prosecutors. Meanwhile, the mayor’s silence is inexcusable. He must explain not only how this spending could have escaped his notice but also what his dealings were with Mr. Thompson.