AN EXECUTIVE in a D.C. accounting firm Thursday became the 40th person convicted of federal charges since 2011 in multi-pronged investigations by the U.S. attorney’s office of public corruption in D.C. government. He’s not likely to be the last. The probe seems to be picking up momentum. Hopefully, that will means answers — finally — to questions of how far into government the corruption extends and, most pointedly, whether Mayor Vincent C. Gray (D) is implicated.

Lee A. Calhoun pleaded guilty in U.S. District Court to helping to disguise the source of more than $150,000 in campaign contributions.

“Today’s guilty plea reveals how a D.C. accounting firm was converted into an assembly line for illegal campaign contributions,” said U.S. Attorney Ronald C. Machen Jr. He described a scheme dating to 2002 that funneled illegal contributions to a variety of federal, municipal and other political campaigns. Hours later, Mr. Machen’s office filed a criminal information (generally signifying a plea agreement) against a Pennsylvania businessman alleging that he, too, made illegal straw donations. The moves come close on the heels of the case against former D.C. Council member Michael A. Brown and Mr. Machen’s statement to The Post’s Robert McCartney that “you are beginning to see significant developments, and I expect that we will continue to be busy.”

The significance of Mr. Calhoun’s involvement and the action against Stanley Straughter , the Pennsylvania man, centers on their association with Jeffrey E. Thompson, who owned companies that held major D.C. contracts. Mr. Thompson has not been charged and he has not been identified by name in court documents, but it’s clear he is the company executive who prosecutors allege reimbursed the straw donors for contributions made in their name. Mr. Thompson has emerged as a central figure in the alleged “shadow campaign” that used straw donors as well as $650,000 in hidden money to help elect Mr. Gray as mayor in 2010. Prosecutors have contended the secret, illegal campaign funding was “coordinated” with members of Mr. Gray’s campaign but have not said that the mayor, who denies any wrongdoing, had knowledge of the activity.

When allegations first surfaced in 2011 — minor-party candidate Sulaimon Brown said he was given cash and promised a city job by the Gray campaign for his attacks on then-Mayor Adrian M. Fenty — Mr. Gray was adamant that he had done nothing wrong. The U.S. attorney showed in subsequent charges against people associated with Mr. Gray’s campaign that there was truth to Mr. Brown’s charges. But citing the ongoing investigation and his attorney’s advice, the mayor has refused to discuss any details of his campaign. It’s unclear if he plans to run for reelection; the primary is less than a year away.

Mr. Gray’s silence may serve the interests of someone under federal scrutiny, but it does not help the District. It’s not enough to keep government running; citizens have a right to know what happened in the last election. It will be unfortunate if that information has to come from the U.S. attorney, but that will be better than no information at all.