In this excerpt from El Narco: Inside Mexico's Criminal Insurgency, journalist Ioan Grillo explains Sinaloa cartel kingpin Joaquín "El Chapo" or "Shorty" Guzmán Loera's relationship with federal agents.

The Sinaloan cartel of Chapo Guzmán and Mayo Zambada, they say, became emboldened by an alliance with federal officials to attempt a takeover of all of Mexico's trafficking supported by federal troops.
Chapo Guzmán then helped arrest his rivals, such as the Beard's brother Alfredo Beltrán Leyva, whom soldiers nabbed in Culiacán on January 21, 2008.
In reaction, the afflicted capos hit back against federal forces because they were working with Chapo.
This accusation was put out on hundreds of messages, or narcomantas, written on blankets and dangled from bridges.
A typical note, hung up in Juarez, said:
"This letter is for citizens so that they know that the federal government protects Chapo Guzmán, who is responsible for the massacre of innocent people ... Chapo Guzmán is protected by the National Action Party since Vicente Fox, who came in and set him free. The deal is still on today ... Why do they massacre innocent people? We invited the government to attack all the cartels."
mantas el chapo mexicoScreengrabA typical 'narcomanta' hangs from a bridge in Mexico.
The government decries such accusations as the scrawling of ignorant gangsters who don't even sign their names. [Then president Felipe] Calderón urged the media not to reprint such narco propaganda. And as I have said, no solid evidence links Calderón to the Sinaloa cartel.
But there is certainly evidence that some federal officials supported Chapo Guzmán's offensive. Toward the end of 2008, a government probe code-named Operation Clean House uncovered a network of twenty-five federal officals on the payroll of the Sinola Cartel.
\Among them were soldiers, federal police commanders, and detectives.
el chapo guzmanGerardo Magallon /AFPThis photo from July 10, 1993 shows drug trafficker Joaquin Guzman Loera "el Chapo Guzman" at the Almoloya de Juarez, Mexico, maximum security prison
However, contrary to the conspiracy theory, evidence suggests that some of these federal forces worked with Chapo Guzmán's rivals.
As part of the same cleanup operation, police arrested fifty agents allegedly working for the Beard Beltrán Leyva.
Felipe Calderon mexicoReutersMexico's President Felipe Calderon speaks during a news conference on the second day of the G20 summit in Los Cabos June 19, 2012.
As I have said, I prefer the cock-up theory to the conspiracy theory.
Calderón may be honest, but he declared war on drug cartels with a rotten state apparatus, one that he could not fully control.
Behind his push, police and soldiers hit gangsters harder than ever before, but these enforcers were still susceptible to bribes.
As a result, Calderón's offensive just threw oil onto the fire.
Drug violence had steadily been rising since 2004. And like water over a flame, this violence finally came to the boil.
Republished with permission from El Narco: Inside Mexico's Criminal Insurgency by Ioan Grillo. Copyright © 2011 by Ioan Grillo. Reprinted by arrangement with Bloomsbury Publishing. All rights reserved.