- The tunnel used in the prison escape likely took about a year to build, Mexican official says
- Tunnels have long been a mainstay of Joaquin "El Chapo" Guzman's operations
- Authorities say the Sinaloa cartel kingpin used a tunnel to bust out of prison
Throughout his reign at the helm of one of Mexico's most ruthless cartels, tunnels have been a mainstay of how the notorious drug kingpin hid out from authorities hot on his trail and built an empire that landed him on Forbes magazine's list of the world's richest moguls.
Here's a look at some of the Sinaloa cartel's most infamous underground passageways to date:
After Guzman made his getaway from Mexico's Altiplano prison over the weekend, authorities say they made a shocking find underground: a lighted and ventilated tunnel, replete with tracks and a modified motorcycle inside.
The tunnel, Mexican National Security Commissioner Monte Alejandro Rubido said Sunday, began with a 50 x 50 centimeter (20 x 20 inch) opening inside the shower of Guzman's cell that connected to a vertical passageway going about 10 meters (33 feet) underground.
The passageway, outfitted with a ladder, led to a tunnel that was about 1.7 meters (5.5 feet) tall and more than 70 centimeters (28 inches) wide.
Inside the passageway, investigators found what Rubido described as an "adapted motorcycle on tracks that was likely used to remove dirt during the excavation and transport the tools for the dig."
One Mexican official estimates the tunnel took about a year to build, and that whoever built it took out about 350 truckloads worth of sand and dirt.
The passageway stretched for more than a mile and ended inside a half-built house. Crews started building the house in December, then stopped a few months later, according to a farmer who lives nearby. The facade appeared to be finished around February or March, the farmer said, but workers kept moving dirt around the property for months -- until Friday, when all of them were gone.
Who helped Guzman build the tunnel, and did prison workers play a role?
Mexican President Enrique Peña Nieto said that's something authorities are investigating.
Analysts say there's little doubt that officials inside the prison were part of the plot.
"You cannot build a mile-long tunnel and get into this without some level of corruption," said journalist Ioan Grillo, author of "El Narco: Inside Mexico's Criminal Insurgency."
One former drug smuggler told CNN on Sunday that it's clear authorities weren't looking for tunnels around the prison before Guzman got out -- a sign they weren't concerned about keeping the notorious drug lord in custody.
"Here's a guy who time and again has proved he can build a hole in the ground," said Brian O'Dea, a one-time smuggler who detailed his experiences in the drug trade in a 2009 memoir. "If they're not looking at every single piece piece of soil around where they have that guy locked up, then they don't have the willingness."
Secret passageways to elude capture
After Guzman was captured last year, authorities said a key discovery marked a turning point in their investigation: seven houses in the Mexican city of Culiacan, connected by secret tunnels that also tied in with the city's sewage system.
When authorities raided one of them, it turned out to be Guzman's main residence in the town of Culiacan. The time it took Mexican marines to get past the house's reinforced steel doors was enough to allow Guzman to escape via a hidden hatch under a bathtub, U.S. officials familiar with the search for Guzman told CNN last year.
The nearest safe house was about 3 kilometers (almost 2 miles) away, but thanks to the network of tunnels, Guzman was able to slip out of sight once again.
They nabbed him later as he slept in a beachside hideaway in Mazatlan, a resort city about 200 kilometers (125 miles) away.
'Super' smuggling tunnels
In 2013, investigators said they'd uncovered a passageway zigzagging underground between San Diego and Tijuana, Mexico, that was so sophisticated they called it a "super tunnel."
The alleged Sinaloa cartel tunnel was 35 feet deep, 4 feet tall and 3 feet wide. It stretched the length of nearly six football fields and had lighting, ventilation and rail system, and it connected two warehouses where prosecutors said they'd seized drugs with a street value of nearly $12 million.
At the time, U.S. Attorney Laura Duffy said she had a warning for smugglers behind the tunnel -- and others like it:
"If you build them, we're going find them," she said, "and if we find them, we're going to destroy them."