It was all a lie. The angry denials, the high dudgeon, the how-dare-you accuse-us bleating emanating from Eric Holder’s Justice Department these last nine months.

Operation Fast and Furious — the “botched” gun-tracking program run by the Bureau of Alcohol, Tobacco, Firearms and Explosives — did, in fact, deliberately allow some 2,000 high-powered weapons to be sold to Mexican drug cartel agents and then waltzed across the border and into the Mexican drug wars — just as Sen. Chuck Grassley and Rep. Darrell Issa, who are leading the congressional investigations, have charged all along.

That’s the conclusion we can draw from Friday night’s nearly 1,400-page document dump, which gives us a glimpse into the inner workings of the Justice Department as it struggled earlier this year to come up with an explanation for the deadly mess — and “misled” Congress.

Now the man who supervised it, Attorney General Holder, will appears before Congress again Thursday to testify in the exploding fiasco. But there’s really only one question he needs to answer: Why?

Why did Justice, the ATF and an alphabet soup of federal agencies facilitate the transfer of guns across the border — without the knowledge of Mexican authorities — when they knew they couldn’t trace them properly?

The scandal erupted late last year, after at least two F&F weapons were found at the southern Arizona scene of Border Patrol agent Brian Terry’s murder. Grassley, the top Republican on the Senate Judiciary Committee, asked Justice for an explanation.

The response was a Feb. 4 letter from assistant AG Ron Weich, who insisted, “The allegation . . . that ATF ‘sanctioned’ or otherwise knowingly allowed the sale of assault weapons . . . is false.” The ATF, Weich went on, “makes every effort to interdict weapons that have been purchased illegally and prevent their transportation to Mexico.”

That letter has now been formally withdrawn. “Facts have come to light during the course of this investigation that indicate the Feb. 4 letter contains inaccuracies,” wrote deputy attorney general James Cole on Friday.

Nice to finally see the government admitting what we’ve known all along — that according to ATF whistleblowers, Fast and Furious was an ill-advised, poorly supervised mess that was doomed from the start.

Fox News recently unearthed a Feb. 3 memo in which ATF agent Gary Styers recounted to his superiors his conversations with Grassley’s investigators: “It is unheard of to have an active wiretap investigation without full-time, dedicated surveillance units on the ground,” he wrote, adding that objections by agents were “widely disregarded.”

Again — why? Perhaps the point was to put the onus for the Mexican drug violence on the American “gun lobby.” The newly released e-mails show Dennis Burke, the since-fired US attorney in Arizona who supervised the operation, furiously pushing back against Grassley and his staff, calling them “willing stooges for the Gun Lobby.”

Holder has insisted he knew nothing about F&F, but the documents show his underlings’ fingerprints. Weich’s original “misleading letter, for example, was edited by Jason Weinstein, a deputy to Assistant Attorney General Lanny Breuer, who forwarded various drafts to his boss.

But Breuer (who reports to Holder) has denied that he had anything to do with drafting or editing Weich’s letter and doesn’t even remember reviewing it before it went to Congress.

So who’s telling the truth?

Meanwhile, Holder spins that F&F was merely a continuation of the Bush-era Operation Wide Receiver, which also lost a few weapons. The difference is that Wide Receiver’s mistakes were inadvertent: That gun-tracking program was under tight surveillance and — unlike F&F — was a joint venture between the US and Mexican authorities.

It’s time for the months of lies to end — but don’t hold your breath. The administration recently sealed the court records relating to agent Terry’s murder and — a year later — the one man arrested hasn’t been tried.

So far, three presidential candidates, a couple of senators and more than 50 congressmen have called for Holder to resign. If he can’t answer the one question that matters — why — that number ought to include his boss.