THE FUTILITY of D.C. Mayor Vincent C. Gray’s attempt to turn the page on the scandal that surrounds his 2010 election was underscored with a report last week that federal prosecutors are nearing a plea agreement with a businessman who is allegedly central to the corruption. It is hard to move on when so many questions are still unanswered, foremost being what — if any — role the mayor played.

If indeed there is a deal in the works that can help shed light on the troubling events of four years ago, we hope it becomes public before D.C. voters have to make the critical choice of a Democratic nominee for mayor. Early voting in the April 1 primary is about a week away, on March 17, and time is fast running out.

The U.S. Attorney’s Office declined comment on the report by The Post’s Ann Marimow and Carol Leonnig that the defense team for Jeffrey E. Thompson has been sharing information with investigators as part of a possible plea negotiation that would resolve any case against him without a trial. Mr. Thompson, a prominent businessman who had major city government contracts, is alleged to have directed more than $650,000 to a secret, illegal “shadow campaign” that benefited Mr. Gray in his 2010 primary victory over former mayor Adrian M. Fenty (D). Seven people connected to Mr. Thompson or the Gray campaign — including three longtime friends of the mayor — have pleaded guilty to federal charges in the long-running probe.

Mr. Gray has denied any wrongdoing. But he has been evasive about details of his campaign or his knowledge of events. He has declined to meet with the federal investigators. Mr. Thompson, according to the Post report, is seen by prosecutors as key to understanding Mr. Gray’s knowledge or involvement in events. Attorneys for Mr. Thompson have declined comment to reporters.

There’s no question the issue is central to the upcoming primary. Seven challengers — including D.C. Council members Muriel Bowser (Ward 4), whom we have endorsed, Jack Evans (Ward 2), Tommy Wells (Ward 6) and Vincent Orange (At Large) — are facing Mr. Gray. A Post poll in January showed 54 percent of adults doubt Mr. Gray’s honesty and trustworthiness, and nearly three in four Democratic voters say the ongoing federal investigation into the 2010 campaign will play at least some role in their choice for mayor.

Chuck Thies, Mr. Gray’s campaign manager, told us the campaign had no views about the timing of any possible development. “That’s up to the Justice Department,” he said, reiterating that the mayor has done nothing wrong.

However U.S. Attorney Ronald C. Machen Jr. proceeds, he likely will be second-guessed. Action before the election could bring charges of an attempt to influence the election, while waiting until after the election could be seen as holding back information. It’s not an ideal situation, but if there is to be a development in this case, we hope it will occur in a timely manner that helps voters but affords Mr. Gray and his challengers some opportunity to respond.