This is the last of three adapted excerpts from Ioan Grillo's new book, "El Narco: Inside Mexico’s Criminal Insurgency," released by Bloomsbury Press. In the book, Grillo interviews an American agent named Daniel who infiltrates a drug cartel. Here, his big bust finally goes down.

Editor's note: Strong language used throughout the excerpt may not be suitable for all readers.

Several years into this work, Daniel built up his huge case in Panama.

He flew down to Central America’s skyscraper paradise, packed with businessmen and criminals from all over the planet; glitzy discos, sparkling casinos and high-class prostitutes, all in a sweltering tropical climate.

Like most big cases, this one started with an informant — a Colombian who inherited a transportation company from his father. The man introduced him to major traffickers, and Daniel built up the relationship from there.

Modern drug traffickers contract a lot of their transportation work out to freelancers. This saves them the hassle of owning so many ships or airplanes, and cuts down the number of their own people close to the product. And this all helps create the diverse structure of cartels, so much tougher to bring down than all encompassing organizations.

Daniel posed as one of the freelancers tendering transport services — offering them a price per ton to move cocaine on his ship. That way, the traffickers would put a huge amount of product onto a boat that the DEA was really controlling — and give the agents a pile of their cash.

It is a pretty simple sting when you break it down; but it was on an aggressive scale that the cartels hadn’t caught onto.

To be convincing, Daniel had to build up his role as freelance drug trafficker – his alter ego. He shows me a photo of himself in that character. He has his long hair with a bandana tied round it and a wild look in his eyes.

“I created somebody else but very realistic so I didn’t fuck it up. The difference between that guy and me (he clicks his fingers) — it could be me right now. That is the problem. He is a lot like me. I grew up so raw that it is nothing. People ask me, ‘Are going to go into your mode?’ What mode? I am that fucking guy.”

Daniel rented out a huge suite at an old Panama hotel where all the traffickers hang out. He would also go to the best table-dance clubs and let himself be seen throwing money round. It was all part of being convincing.

(The DEA footed the bill for his hotel – but the strip clubs came out of his own pocket.) He went back and forth to Panama over several months building relations with the traffickers. He would meet them at flashy restaurants. First he met with one, then two, then four.

Then one time he sat with eight Colombian traffickers.

“It is a little concerning because that is a lot of eyes looking at you. I broke the ice and talked about a soccer game. I follow a lot of soccer — I like Arsenal and I like Boca Juniors — and then we talked for hours. They are very eager and hungry for money.

I like things that have an adrenalin rush and that is one of them. Undercover is a rush, because you don’t know what is going to happen, whether you are going to come back or not.”

Daniel was getting close. But the work was taking a toll on him. He began to lose his own identity; to get lost in the world of flash Colombian traffickers with their entourages of beautiful women. Who was he really? The undercover cop or the trafficker? Before going out to meets, he got scared. What if he messed up and let onto who he really was? One thing that kept him grounded, he said, was a record by New York producer Moby, which contained tracks with deep, melancholy beats.

“I would listen to this song and get extremely hyped up. This is how I found the motivation inside of me to get all my energy and my adrenalin to do what I needed to it. I would take a cab from the hotel room to go and meet with the bad guys and I knew that I had to go there and win. That is all I had to do. I had to go there and confuse them and convince them that I was who I said I was.

I never took my eyes off them; never looked down. I was very positive and affirmative with the things that I said. When I looked how I looked then, I would believe me too. I had a very dry look. I spoke very sharp and to the point. I had a look that said, ‘If you fuck me, you know we are going to go toe to toe.’ ”

That was when Miami Vice hit the cinema; with the same scam he was selling. Watching it he was tempted to run for his life. But he stuck at it. And thankfully, it seemed the Colombians didn’t see the movie.

Finally came the day for the deal. The Colombians bought his story, and handed over nearly four tons of cocaine and a suitcase of money. The drugs were put onto a 35-foot cargo vessel used to lay cable on the seabed. It had enough fuel to get to Spain. The Colombians put one guy out to sea with the stash — plus Daniel and the crew were on board. The boat hit the waves. And then — BANG — the navy seized it.

Daniel had taken down drugs worth hundreds of millions on the street.

Panama was hard. But another job left a deeper scar in Daniel — when he pulled the same scam again on Mexican drug traffickers.

The sting was set up in a city on the U.S.-Mexico border. Daniel gradually built up connections with a major smuggling operation. He offered them a truck to move drugs into the United States. The idea was to seize the drugs, the money and to get all the crooks in the warehouse where the truck was going.

Daniel’s main contact with the smugglers was a legal student in his mid twenties. The young man was taking part in the trafficking to pay his way through the law school. In six more months, he would receive his credentials. The student fell for Daniel’s story and bought the transport services. He had inadvertently putting the drugs of his bosses into the hands of the DEA.

The movement of cargo went down — and Daniel got a call from the student. The cartel had taken the student hostage in a house as a ransom for the delivery of the drugs.

“He called me and begged for his life through a phone in a room where I could hear him getting beaten down to his very last breath. We took everything down: we delivered the goods; we arrested the people who were receiving it. But I never saw him (the student) again. They found his car and his wallet on the street.”

A few days later, Daniel got a call from the student’s parents. They had found their son’s phone and seen Daniel’s number in it. They were asking for any information to recover their son’s body.”

“The parents asked if I knew where their kid was so they could give him a decent burial. That really sends it home. It really makes you feel like shit, because what if that was your kid? You have so much love for your kid that you would drag them out of the ground. I think that really set the tone for me, like, ‘What the fuck are you doing?’ You are killing people. You are setting up people to fail.”

Daniel started to feel doubts. He asked for permission to leave undercover and become a regular agent – at least for the short term. It is a few months after this that I meet him for beer and pizza.

“I cut all my hair. I wanted a break. I wanted to change who I was.”

Part One: Meet DEA Agent Daniel

Part Two: Dying for Nothing