Opinion writer

You had to read to the end of Sunday’s Post editorial “ D.C.’s reticent mayor to discover the most salient piece of information to date related to Vincent Gray and the federal investigation into his 2010 Democratic mayoral campaign.

The grabber: “The problem . . . is that Mr. Gray apparently isn’t talking to federal prosecutors, either. Sources told us that he has declined several requests for a meeting.”

Two days later, WRC-TV’s Tom Sherwood added to the mystery by reporting that his sources also said that Gray had declined on several occasions to meet with prosecutors.

An alert citizen might inquire: “Didn’t Gray call for an investigation of his own campaign?” and “Didn’t he say last July that ‘we will continue to work with the investigation’?” Why, yes, he did.

Gray’s Wilson Building supporters take him at his word. I can almost hear them shouting, “Who wants to get to the bottom of what happened more than Vince Gray?”

Well, for one, U.S. Attorney Ronald C. Machen Jr., as well as his hardy band of assistant prosecutors, FBI agents and tax experts.

Why won’t Gray sit down with the feds and tell all he knows about the 2010 mayoral campaign? If he has nothing to hide, what’s holding him back?

Evidence uncovered thus far justifies concern.

More than $650,000 of unreported money was illegally used in a behind-the-scenes effort to help Gray wrest the mayoral nomination from incumbent Adrian Fenty.

Gray said that he knew nothing about that shadow campaign and that he has done nothing wrong.

Federal authorities, understandably, are eager to engage Gray in an exchange of views about that matter.

But Gray, reportedly, has buttoned up.

Which gets us to another question about Gray’s reported non-cooperation: What does the law require? This is a vital point that every citizen, regardless of his or her feelings about the mayor, should keep in mind.

You do not have to answer questions from the police, FBI or U.S. attorney just because they ask. The Constitution gives you the right to remain silent. You also have the right to have a lawyer present if questioned.

It’s easy to overlook the possibility — sometimes remote, sometimes real — that when confronted by the authorities, you may say something that, in your mind, is insignificant — only to find it taken out of context and used against you or manipulated and used against someone else.

There’s also a stiff price to pay if, when questioned by the feds, you lie or mislead.

On the other hand, they can’t get you for what you don’t say.

The right not to talk is precious. It is a right that extends to the homeless person on the street, the banker out on the town, the student walking home from school and the mayor. To say you don’t want to be interviewed is no admission of a crime.

In Gray’s case, the federal government is not without means to seek his testimony even if he is not the target of a grand jury investigation. If Machen thinks Gray may have knowledge or information related to the shadow campaign or other campaign violations, he can issue a subpoena for Gray’s testimony. Should that happen, a host of other questions and reactions will kick in concerning the focus and direction of Machen’s investigation, but lawyers and courts can sort that out.

Legally, therefore, Gray risks very little with silence. Politically, however, it will prove costly. Politicians can’t tell the public to trust them and then refuse to cooperate in an official investigation.

The point is, a federal grand jury has wide-ranging powers, and Vincent Gray is not beyond its reach.

That said, there are reasons that folks associated with Gray’s campaign, and perhaps even Gray himself, might be sleeping poorly these days.

To cite just two:

●Former Gray campaign aide Howard Brooks, who was sentenced to two years of probation for lying to federal agents about campaign-finance violations, wore a government-supplied recording device that captured Thomas Gore, another Gray campaign aide, admitting on tape that he destroyed a ledger of illegal campaign payments. Query: Have the feds asked anyone else involved with Gray’s campaign to wear a recording device? Answer: Almost certainly yes.

●The D.C. Office of Campaign Finance, by law, should have a public record of all people who donated to Gray’s 2010 campaign. The bad news: It doesn’t. The good news: The feds are learning the identities of those donors, as well as who acquired their contributions off the books, why and how.