Our nation’s capital has a real whodunit on its hands. But this is no tale of fiction.

It is a sad account of public corruption. As our drama unfolds, clues abound. Some villains have been caught, but not all have been exposed.

The theme song playing in the background of this D.C. story is Barrett Strong’s 1959 hit: “Money (That’s what I want).”

“The best things in life are free,

but you can give them to the birds and the bees,

I need money

that’s what I want.”

Some say that money is not the most important thing in the world. Love is. Unfortunately, our D.C. pols love money. Hence our corruption saga.

Solving the puzzle is the responsibility of U.S. Attorney Ron Machen and his team of assistant prosecutors and FBI agents. Machen has provided concrete evidence of wrongdoing. To recap the year’s events thus far:

●Former D.C. Council member Harry Thomas Jr. is performing extended involuntary public service at a federal penitentiary in Alabama after pleading guilty to ripping off D.C. tax dollars.

Kwame Brown’s status changed abruptly from city legislator to felon in June after his conviction for bank fraud. Sentencing of the former D.C. Council chairman is set for September.

●Top aides to Mayor Vincent Gray’s 2010 election campaign — campaign treasurer Thomas Gore and adviser Howard L. Brooks — pleaded guilty to felony violations.

●So has Gray’s longtime friend and campaign aide Jeanne Clarke Harris.

But the mystery is far from over.

As I have written before, inquiring minds want to know: Who is “Co-conspirator #1”?

This individual, according to Machen and court documents, schemed with Harris to create a $653,000 campaign fund to elect Gray. Co-conspirator #1 also bankrolled the illegal operation, Machen said.

Some have speculated that Co-conspirator #1 is D.C. businessman Jeffrey Thompson.

This much is known: Federal agents raided Thompson’s home and offices in March and took away loads of stuff.

Can the confiscated materials stand up to front-page scrutiny? Do fruits of the raid have a bearing on the “shadow campaign” fund or other possibly unlawful activities? Co-conspirator #1 knows. So, presumably, do prosecutors.

Which gets us to mysterious “Person A.”

Howard Brooks, who pleaded guilty to lying to federal agents, has owned up to giving a fringe candidate in the 2010 mayoral contest, Sulaimon Brown, money to stay in the race and continue launching verbal attacks on then-Mayor Adrian M. Fenty. Brooks was no freelancer; he advised the feds that he was “instructed” to pay Brown by “Person A.” Who, pray tell, is that?

Speculation is rampant. Could it be Lorraine Green, also a close friend of Gray’s and chairwoman of his 2010 campaign and transition committees? Brooks was Green’s lieutenant in the campaign. Green has denied knowing about Gray campaign funds being given to Brown, and two close friends of hers adamantly maintained to me that she is not the person who “instructed” Brooks to pay Brown. So, if not Green, then who? Gray denies knowing about the payments to Brown. Who’s left? What does Machen know? Can he prove it?

Let’s look again at the individual who developed the plan to conduct a shadow campaign on Gray’s behalf. Harris said in court that while “Co-conspirator #1” provided the money, the scheme was dreamed up by someone else. Who is the schemer? Again, what does Machen know, and what can he do about it?

The thirst for ducats drove Harry Thomas, both Browns and some Gray campaign staffers.

That same thirst is the driving force behind all of the wrangling and backdoor maneuvering over the city’s lottery contract, the awarding of which four years ago is being investigated by the FBI for possible corruption.

That $228 million contract had the hustlers salivating. Remember our theme song: “I need money, that’s what I want.”

Money represented a glide path to easy street. Why?

The lottery contract winner was expected to be a national or international company because of the required expertise; political pressure required the winner to have a local partner who could pass political muster. That means winning clearance from the D.C. Council, which approves all city contracts over $1 million.

With the council’s blessing, the local partner faced a future filled with ka-ching sounds, all for doing nothing except having a local address and, oh yes, some well-connected non-European faces.

Now that’s worth fighting and lying for, some thought. So they did.

Can’t wait to reach the end of this latest, and perhaps greatest, chapter of our corruption drama . . . when sentencing is pronounced on all.