THREE YEARS ago, a former fringe candidate for mayor, Sulaimon Brown, alleged that the campaign of D.C. Mayor Vincent C. Gray (D) gave him cash and a high-paying city job as rewards for hectoring incumbent Adrian M. Fenty during debates.

Mr. Gray issued a flat denial. His supporters expressed skepticism. Mr. Brown was labeled a nuisance, annoying and not credible.

But Mr. Brown, whatever his failings, was proved right about a quid pro quo that turned out to be just the tip of the iceberg of backroom deals, illegal cash and other sordid events that contaminated Mr. Gray’s campaign four years ago.

We recollect these facts in light of Mr. Gray’s challenge that he, and not disgraced businessman Jeffrey E. Thompson, is to be believed about whether Mr. Gray knew about the illegal “shadow campaign” that helped secure his election four years ago.

The truth of Mr. Thompson’s claim that Mr. Gray personally asked him to finance the campaign scheme has yet to be determined. Mr. Gray says Mr. Thompson is lying. Since the start of the scandal, we have urged Mr. Gray to be forthcoming about the activities of his campaign and his knowledge of events. Citing the advice of his attorney, he declined comment and evaded questions, even as prosecutors collected guilty pleas from an ever-tightening circle of friends and campaign associates. He wouldn’t say when he first learned of the shadow campaign or whether there had been cause for him to be suspicious. The mayor became more talkative after Mr. Thompson’s claims were aired Monday by federal prosecutors, but the answers are far from reassuring.

Consider Mr. Gray’s acknowledgment that he referred to Mr. Thompson as “Uncle Earl” to shield his identity. “I thought it was because of him not wanting to be seen as legitimately raising money for my campaign. That’s true. But there was never any illicit secrecy associated with that,” he told WRC-TV’s Tom Sherwood. How did Mr. Gray think Mr. Thompson would contribute to his campaign if he didn’t want to be seen as doing so “legitimately”? As council chairman in 2010, did it not concern Mr. Gray that a major city contractor was seeking to hide his campaign help?

Since the mayor is now willing to answer more questions, maybe he can go back to where this all started. Why did his administration offer a $110,000-a-year job to a man seen as a nuisance and annoying and not credible?