Fran Miller, once an insider from Mark Green’s mayoral campaign, came forward to tell prosecutors in Brooklyn what she knows about attempted money laundering and paying cash for fliers warning of the ties of Mr. Green’s opponent, Fernando Ferrer, to the Rev. Al Sharpton. Ms. Miller is now helping clean up the cesspool of politics in Brooklyn, where judgeships may be sold, endorsements auctioned and dirty tricks abound. Ms. Miller, who has long thought of herself as an activist on the side of reform, is now playing a new kind of role in reforming politics.

Other players have already begun to share their experiences. Ruth Messinger has described how, in 1997, when she was running for mayor, the Democratic Party boss at Brooklyn, Clarence Norman, asked her for more than $200,000 in “contributions” and “street money” for his endorsement. Ms. Messinger said no. After it was reported that Mr. Green’s campaign paid $245,000 to Mr. Norman’s Thurgood Marshall Democratic Club, on the eve of its endorsement of Mr. Green’s campaign, Ms. Messinger told the New York Post of her experience.

Two judges have also stood up and told prosecutors how they were coerced to hire certain vendors and consultants if they wanted Mr. Norman’s support in their bids for re-election — and if they expected to be on the party’s palm cards on primary day. Karen Yellen and Marcia Sikowitz should be commended. They have helped illuminate the system of “tollbooths” judges have to stuff with money if they want re-nomination. They have helped the city learn of a pattern and practice by Mr. Norman’s political organization. They have named certain vendors, such as William Boone III and Ernie Lendler, as the exclusive gatekeepers of the machine.

Ms. Miller, however, is the first to speak from the perspective of an insider, which is what makes her contribution so valuable to the city and prosecutors. Plenty of others could help. Twenty Brooklyn pols and powerbrokers were at the now-famous lunch, which took place October 4, 2001 at a seafood restaurant in Sheepshead Bay, and at which there was open talk of circulating against Mr. Green’s opponent in the Democratic primary that year, Mr. Ferrer, literature highlighting his ties to Rev. Sharpton. Democratic members of the state Legislature and the city council were present.

Now there’s nothing in and of itself illegal about plotting to disseminate controversial campaign fliers. One contained a reprint of a cartoon by the New York Post’s cartoonist Sean Delonas; the cartoon showed Mr. Ferrer kissing Rev. Sharpton’s posterior. There were also mass phone calls made, suggesting that if Mr. Ferrer were elected, Rev. Sharpton would pick the next police commissioner. But once the expenditure of publicly financed campaign contributions is involved, the law requires an accounting.

By our lights, these kinds of campaign finance regulations are unconstitutional. But at the moment, they are the law and deserve to be obeyed. Prosecutors are looking at whether fear of being publicly connected with this kind of literature led to a scheme by some campaign workers to try to disguise, or launder, the source of the cash that went into the effort.

During the election in 2001, Mr. Green said his campaign had nothing to do with the fliers, but it was a serious enough question that he appointed his campaign manager, Richard Schrader, to conduct an investigation. Though Mr. Schrader’s investigation shed little light on the matter, we now understand that three workers in Mr. Green’s campaign have told the district attorney of Kings County that senior campaign officials authorized the fliers — and the phone calls that were made on the eve of the primary. No public filing has accounted for the payments for either the fliers or phone calls.

At a time when America is at war, when the national economy is teetering between expansion and collapse, and when the state and city budgets are in crisis, this might seem like small beans. But there are those of us who see it as a once-in-a-generation opportunity to clean up politics at Brooklyn and to uncouple, finally, the courthouse from the clubhouse. It is what we like to think that idealistic reform politics is all about in a city like New York. And it is no doubt why Ms. Miller has come forth to set an example.