Behind the story: What it's like to interview members of Mexico's notorious drug cartels

W5 | Narco Jungle: The Death Train, Part 4 W5's Avery Haines is inside Juarez where she speaks with one of the human smugglers known as 'coyotes' in Part 4 of The Death Train.

CIUDAD JUAREZ, MEXICO — This is part four of a five-part series following the harrowing journeys of migrants who risk their lives crossing the Darien Gap and riding atop Mexico's notorious 'Train of Death.' W5 Investigative Unit Managing Editor and Senior Correspondent Avery Haines explores migrant smuggling, which is turning into a financial windfall for human smugglers known as 'coyotes.'

I’ve interviewed several cartels over the years, from high-ranking drug bosses to low-level sicarios, or executioners.

Each time there have been some heartstopping moments.

In Cancun for the W5 documentary, "Narco Riviera," I tried not to let my panic show when my interview with a Sinaloa drug boss was interrupted by a knock at the door of the narco “safe house.”

For Narco Avocado I interviewed Mexico’s most ruthless cartel, Jalisco New Generation (CJNG) in an avocado orchard deep in their territory.

And for last season’s documentary on the Darien Gap, Colombia’s Gulf Clan cartel interview shed new light on their lucrative human smuggling business.

For my latest investigation, "Narco Jungle: The Death Train," I convinced a human smuggler to talk to me about the fees they charge migrants to get them across the border. He tried to portray himself as a humanitarian helping migrants reach their “American Dream.” He is not.

Cartels endanger migrants at every stage of their journey with kidnappings, torture, and extortion.

InSight Crime, an organization that researches organized criminal organizations in Mexico and South America, estimates there are “several hundred crime groups” operating across Mexico, many of which are supplementing their core business of drug trafficking with migrant smuggling.

Migrants we interviewed in Mexico described being “taxed” as they made their way through different cartel territories.

Those who pay are given coloured wristbands and allowed to continue through their region. Those without money have shared stories of being locked up and forced to contact family members or friends to pay the cartel fees.

The U.S. Homeland Security Committee estimates that human trafficking and smuggling is a US$13 billion a year industry for the cartels.