It’s one of the longest-running congressional investigations of our time: the probe into Fast and Furious. It was the government’s secret operation to watch as thousands of weapons were trafficked to Mexico’s killer drug cartels.

In many respects, the story began when federal agent John Dodson agreed to an interview with investigative journalist Sharyl Attkisson in March 2011. It was highly unusual, if not unprecedented, for a sitting federal agent to speak out in such a strong way.

In the latest episode of “Full Measure,” Attkisson catches up with Dodson six years later.

Dodson: Part of my mission with the [Bureau of Alcohol, Tobacco, Firearms and Explosives] in Phoenix was to combat a legal firearms trafficking to the Mexican drug cartels. Somehow, in order to achieve that goal, the strategy that had been adopted was to facilitate and allow the illegal firearms trafficking to the Mexican drug cartels. We were essentially flooding the border region with firearms from the U.S. civilian market, and then tracking and tallying the results as they were used in crimes on both sides of the border.

Attkisson: “We” meaning federal agents, who are supposed to be stopping the trafficking?

Dodson: Yes, ma’am, meaning the federal agency that was in charge of combating that very thing.

Dodson had objected internally to the dangerous practice of “gunwalking” secretly allowed by the ATF. But his objections fell on deaf ears.

Attkisson: Was the final straw Brian Terry’s murder?

Dodson: Yes. When Border Patrol Agent Brian Terry was killed, I immediately noticed that my agency was attempting to cover up any link between the investigation and the strategy that we employed and the death of Agent Terry.

Illegal immigrants armed with Fast and Furious rifles gunned down Terry in Arizona in December 2010 near the Mexican border. Dodson says Department of Justice officials frantically worked to cover up the killers’ links to weapons trafficked as part of the secret federal case. He agreed to an interview with Attkisson for CBS News in March of 2011.

(Attkisson’s interview with Dodson on CBS aired March 3, 2011.)

Attkisson: Dodson’s job is to stop gun trafficking across the border. Instead, he says he was ordered to sit by and watch it happen. Investigators call the tactic letting guns “walk.” Dodson’s bosses say that never happened. Now, he’s risking his job to go public.

Dodson: I’m boots on the ground here in Phoenix, telling you we’ve been doing it every day since I’ve been here. Here I am. Tell me I didn’t do the things I did. Tell me you didn’t order me to do the things I did. Tell me it didn’t happen. Now you have a name on it. You have a face to put with it. Here I am. Someone now, tell me it didn’t happen.

Attkisson: When you stepped forward, what did you think and hope would happen?

Dodson: When I stepped forward, I thought it would all come to a screeching halt, and that the case would be shut down, the policy would be abandoned, and it would pretty much be over with very, very quickly, as soon as word got to the right people. I was very surprised to learn otherwise.

Attkisson: What did happen?

Dodson: Well, originally the Department of Justice issued what was a letter denying the allegation, categorically denying the allegations. And from that point on, there was a congressional hearing and obstruction and document hiding and it seemed like everything that the United States government could do at the time to avoid showing the allegations that was alleged and proving them and … still continuing to deny that there was any nexus between the investigative strategy and Agent Terry’s death.

The supposed goal of the government’s gunwalking was to see where the weapons ended up and make a big case that took down Mexican cartel leaders. That never happened. Instead, the guns were used in crimes on both sides of the border. Attkisson identified a dozen other federal cases in which agents allegedly allowed guns to walk in places like Florida, New Mexico, Texas, and Arizona, with names like Too Hot To Handle, Wide Receiver, and Castaway.

In a bipartisan vote in 2012, the House of Representatives held Attorney General Eric Holder in contempt of Congress for refusing to turn over documents in the Fast and Furious case. President Barack Obama blocked Congress from getting the documents by using executive privilege the one and only time of his presidency. Eighty thousand pages were later released under a court challenge.

At a little-publicized hearing earlier this month, House Oversight and Government Reform Chairman Jason Chaffetz, R-Utah, said Congress is still trying to convince the Justice Department to hand over outstanding documents.

Chaffetz: Litigation is ongoing as it continues its unprecedented stonewalling and I’m sorry to report under the Trump administration this has not changed. This has not changed.

Dodson testified at the hearing alongside Terry’s mother, looking back at his decision to blow the whistle.

Dodson: That single action … went from being an agent of the government … to enemy of the state.

Members of both parties, including Rep. Trey Gowdy, R-S.C., and the incoming chairman of the House Oversight Committee, said they still don’t think they have all the answers as to what was really behind Fast and Furious.

Gowdy: I’m just struggling to understand how this ever could have turned out any other way. As soon as the gun leaves the parking lot, unless you’re maintaining constant surveillance, then you’ve lost the gun. And then if it crosses the border, God knows what you’re going to do with it. And then when you learn they didn’t even let our Mexican counterparts in law enforcement know what was going on. This is the most imminently predictable tragedy that I’ve been connected with since I’ve been in Congress.

Attkisson: What are some of the outstanding questions today?

Dodson: Well, I think that some of them, and they all might not pertain directly to the Terry family, is the amount of homicides or murders that have been caused by the firearms that we allowed to be trafficked, what the ultimate cost of this strategy was, I think those numbers have been kept and held.

Although the government won’t release information delineating the crimes that have been committed by criminals using guns trafficked during Fast and Furious, Attkisson found evidence of at least 43 killings, including two U.S. federal agents, three Mexican police, and a terrorist torture kidnapping and murder in Mexico.

Attkisson:  Do you think people are still in place in government who are part of what you call the obstruction or the cover-up?

Dodson: I think they are. I think maybe not in the same exact positions. I think many of them moved around. But there is still a good portion of that system, that mechanism that is still in place.

Attkisson: It sounds like your takeaway is that the public should understand it holds the power and use it.

Dodson: Yes, the public does hold the power. They’re supposed, that’s how our entire system is designed, but if we don’t ask the questions, if we don’t hold people accountable, if we don’t get the explanations that we deserve and the answers that are entitled to us, then we don’t. We, we give those reins of power away, alright? And we’re also subjected to a bureaucracy that is so big and so uncontrollable that it answers only to itself, no longer to us.

In case you’re wondering, Dodson still works at ATF today, though he says he’s been marginalized, retaliated against, and transferred around 11 times in six years.

In April, U.S. officials arrested one of Terry’s alleged killers. Five others have pleaded guilty or been found guilty by a jury in the case. One suspect is still on the loose. Hundreds of guns that the feds allowed to be trafficked to criminals are still missing and unaccounted for.