ReutersIn this excerpt from El Narco: Inside Mexico's Criminal Insurgency, journalist Ioan Grillo explains Sinaloa cartel kingpin Joaquín "El Chapo" 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 ...