In between Colombian drug lord Pablo Escobar and Mexico’s El Chapo, the world’s most powerful drug trafficker, there were the Arellano brothers. In the early 1990s, the Arellano Felix Organization and El Chapo’s Sinaloa cartel fought each other to be the biggest, baddest drug traffickers in Mexico. At one point, the AFO was responsible for 40 percent of the cocaine consumed in the United States. One former lieutenant said that Benjamin Arellano, an AFO leader, was responsible for more killings than the 9/11 terrorists.

When DEA agent Jack Robertson started investigating the AFO in the early ‘90s, the agency thought the inquiry would last six months. It lasted 20 years. For the first time, Robertson went on the record to talk to ProPublica reporter David Epstein about the case that ate up 200,000 man-hours and millions in taxpayer money. One of the biggest questions remains: Was it all worth it? All three of the brothers ended up in U.S. jails, though one will be out in just a few years. But DEA intelligence that might have helped the government pursue El Chapo never was used.

On Thursday, December 17th, at 2 p.m. EST, you asked Robertson — who went on to help take down Lance Armstrong — anything about fighting narco-traffickers and the challenges of federal drug enforcement on Reddit. ProPublica reporter Epstein was also on hand to talk about this never-before-told chapter on the rise of El Chapo, the role the U.S. government played in it and how he found the story.

Read the highlights below, or view the AMA on Reddit.

Questions and answers have been edited for length and style.

What is the extent of cartels embedding themselves into Mexican gov't agencies? Could they be rooted out? – Aximill on Reddit

An agent I spoke with, relaying information from a cartel figure, said that they have people in every branch of the government, especially police, and those people will provide the intelligence they need, and then there are people who are actually overtly advertising themselves from government positions as available to be of use to the cartel. He also emphasized that there are brave people who don't work for the cartels, but that they are in each branch. He added that the line considered corruption among cops is not quite where it is in the US. There are a lot of scams and schemes, but working with cartels is clearly over the line. – David Epstein, ProPublica

Jack, did you watch Narcos and Breaking Bad? If so, what was the most realistic part of each show? What was the most unrealistic? –elizwgreen on Reddit

I'll just deal with Narcos since I just watched the series. I found the level of violence perpetrated by the cartels extremely realistic. The cartels (Mx & CB) make the Sopranos look like girl scouts. This was the case with the AFO, the most violent and brutal cartel I have ever seen. My partners and I interviewed numerous cartel assassins who spoke calmly of their kills, as they were describing the weather. ‚Ķ We met only a few who actually had remorse for what they had done. — Jack Robertson, Former DEA Agent

How was the transition from dealing with a dangerous drug cartel to taking down Lance Armstrong? –lolsfordayz on Reddit

After co-leading the AFO investigation for several years, I began working cases targeting the int'l trafficking of steroids & designer club drugs. … In 2011, I got an incredible job offer to leave DEA and join WADA as their Chief Investigator. It was an interesting and challenging job change, but it combined two passions, clean sport and drug investigations. Working for WADA has been a great experience and assisting USADA on the Armstrong investigation was a tremendous experience. Travis Tygard & Chief Counsel Bill Bock have the most integrity of anyone I have worked with. РJack Robertson, Former DEA Agent

How do you think cartel violence compares to Daesh/ISIL/ISIS violence? It seems like both made a name for themselves by making brutality their brand. How do the cartels use that brand of brutality to achieve their ends? – danielepstein85 on Reddit

[L]aw enforcement agents told me during my reporting that they think there is some one-upsmanship in terms of public brutality between cartels and terrorists at times. And certainly many more people have been brutally killed by cartels. —David Epstein, ProPublica

Yes, violence and bribery. In this investigation we saw the AFO killing/torturing thousands and investing tens of millions in bribe payments. — Jack Robertson, Former DEA Agent

How did you find this story? – thedeadlybutter on Reddit

I was an investigative/science reporter at Sports Illustrated, and was filing public records requests before the 2008 Olympics about Chinese pharmaceutical companies that I thought might be involved in putting illegal or unlisted ingredients into dietary supplements that end up in US stores, often touting benefit for sports performance. Jack was interested in some similar issues, and so I got to know about his work through that. Later on, he began to tell me about his cartel work, and I got really interested, and it started from there. – David Epstein, ProPublica