[suspenseful music]

MARIANA VAN ZELLER: In my quest to expose how American guns are

trafficked throughout Mexico, I never expected

to be headed out to sea.

But as we move deeper into the waters,

these smugglers break down their operation.

The Sea of Cortez is over 700 miles long

but less than 100 miles wide.

That means these smugglers can make the crossing in less

than three hours, completely bypassing

the military checkpoints set up along Mexico's highways.

Right now, they say they're delivering

more and more guns to Sonora directly across the sea.

That's the same heavily contested

territory that Hector in Mexicali

is also sending guns to.

I think we're-- that's it.

I think we're going to that beach over there.

Oh, there were some guys there.

There are some guys actually waiting at the beach.

Or at least one guy that I see now.

And he's coming to greet the boat.

He's all dressed in black with a mask, as well.

Yeah, they're anchoring right there so this is it.

I'm told the man in black is another buyer from Sonora.

[suspenseful music]

Hola.

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: [speaking spanish]

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: [speaking spanish]

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: [speaking spanish]

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: [speaking spanish]

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: [speaking spanish]

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: A month.

[speaking spanish]

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: [speaking spanish]

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: 50 calibers, RPGs.

[speaking spanish]

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: None of this sounds like arming

a criminal organization.

They're arming for war.

[speaking spanish]

CARTEL MEMBER: [speaking spanish]

[upbeat music]

MARIANA VAN ZELLER: I'm told the buyer is

from an affiliated cartel fighting

to regain territory in Sonora.

He's picking up a fresh order, including a pair of customized

handguns for rich narcos who don't just want a weapon,

they want to make a statement.

Sales like this are common for these smugglers.

The market for American assault rifles is exploding.

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: [speaking spanish]

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: [bleep] So they had 200 AK-47s

[speaking spanish] which is what they call them here,

come through here, San Felipe, in just one day last week.

[speaking spanish]

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: Here's where things get interesting.

Remember when I said that you never ask

what cartel someone belongs to?

I didn't.

This guy just decided to tell me that he works for one

of the fastest growing mafias in Mexico, the Jalisco

Cartel, also known as CJNG.

MAN: [speaking spanish]

MARIANA VAN ZELLER: The organization is only about 10

years old, but aggressive maneuvers

and terrifying ISIS-style executions

have helped them dominate underworld

markets across Mexico, becoming the Sinaloa

Cartel's biggest rival.

And the kingpin of these violent upstarts,

perhaps the most dangerous drug lord in the world,

is known as El Mencho.

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: [speaking spanish]

CARTEL MEMBER: [speaking spanish]

MARIANA VAN ZELLER: [speaking spanish]

CARTEL MEMBER: [speaking spanish]