Police agents in San Fernando in the northeastern Mexican state of Tamaulipas aided Los Zetas drug gang in carrying out massacres of hundreds of Central American migrants and others in 2010 and 2011, according to a partially redacted document declassified by Mexico's Attorney General's Office (PGR). Although collusion between local Tamaulipas police and criminal gangs was already well known—US diplomatic cables released by the US government in 2013 discussed it, and locals refer to the police as "polizetas"—this is first time that the PGR has been required to release a document from an ongoing criminal investigation. Previously federal prosecutors had insisted that Mexican freedom of information laws didn't apply to open investigations. The document is now available on the website of the Washington DC-based National Security Archive, along with other relevant documents, including reports from US government agencies and US diplomatic cables released by the WikiLeaks group.

The sentencing last month in a case related to the Sinaloa Cartel's Chicago connection provided further fodder for the increasingly plausible conspiracy theory that the DEA protected Mexico's biggest criminal machine. Federal Judge Ruben Castillo sentenced Alfredo Vázquez Hernández, who had been extradited after serving a sentence in Mexico, to 22 years in prison for shipping 276 kilograms of cocaine to Chicago hidden in railway cars. Federal prosecutors said Vazquez was a top-ranking operative of the Sinaloa synidcate, who arranged airplanes, submarines, trains and trucks to move cocaine from Colombia to Chicago via Mexico. Vazquez was characterized as a lifelong friend of the cartel's now-imprisoned top kingpin "Shorty" Guzmán. Judge Castillo said this hadn't been proved, but stated: "Given the amount, it's nonsensical to think this was this defendant’s inaugural voyage into cocaine trafficking."

On Dec. 13 the left-leaning Mexican news magazine Proceso published an investigative report challenging the government's account of the abduction of 43 students and the killing of three students and three bystanders the night of Sept. 26-27 in Iguala de la Independencia in the southwestern state of Guerrero. Based on cell phone videos, interviews, testimony by witnesses and leaked official documents, the report's authors, Anabel Hernández and Steve Fisher, claim that agents of the Federal Police (PF) were involved in the attack on the students, that the Mexican army was at least complicit, and that the administration of President Enrique Peña Nieto has been covering up the role of federal forces.

The remains of one of 43 students abducted the night of Sept. 26-27 in the southwestern Mexican state of Guerrero have been identified by DNA tests, parents of the missing students said on Dec. 6. Technicians in Innsbruck, Austria, established that one of 14 bone fragments sent them by the Mexican government came from the body of Alexander Mora Venancio, a 19-year-old student at the Raúl Isidro Burgos Rural Teachers' College in the Guerrero town of Ayotzinapa; gang members and municipal police had detained him along with 42 other Ayotzinapa students in Iguala de la Independencia during attacks which also left three students and three bystanders dead. The bone fragments were found in a dump near Iguala in Cocula municipality after three members of the Guerrero Unidos ("United Warriors") gang told federal authorities they had helped burn and dispose of the bodies there.

Hundreds of Mexican immigrants and other activists held actions in at least 47 US towns and cities on Dec. 3 to protest the abduction of 43 teachers' college students by police and gang members in Mexico's Guerrero state in September; each of the 43 students had one of the actions dedicated to him. The protests were organized by UStired2, a group taking its name from #YaMeCansé ("I'm tired now," or "I've had it"), a Mexican hashtag used in response to the violence against the students, who attended the Raúl Isidro Burgos Rural Teachers' College in the Guerrero town of Ayotzinapa. The protesters focused on US government financing for the Mexican government—especially funding for the "war on drugs" through the 2008 Mérida Initiative—but they also expressed outrage over the US court system's failure to indict US police agents in two recent police killings of unarmed African Americans.

In a Nov. 27 address Mexican president Peña Nieto announced that he was sending the Congress a series of proposed constitutional amendments he said were intended to resolve a crisis brought on by the killing of six people and the abduction of 43 students the night of Sept. 26-27 in the southwestern state of Guerrero. According to federal prosecutors, corruption in the municipal government and police in the city of Iguala de la Independencia were behind the violence; the police and the mayor, José Luis Abarca Velázquez, were reportedly linked to the local drug gang Guerreros Unidos ("United Warriors"). Peña Nieto's amendments would end the independence of the police in Mexican municipalities and bring them under the control of state police departments. The president also proposed strengthening laws for the protection of victims. In his presentation Peña Nieto tried to associate himself with popular demands for the return of the 43 missing students by using a slogan repeated throughout the many national and international protests since the attacks: "We are all Ayotzinapa." The missing students and three of the six people known dead attended the Raúl Isidro Burgos Rural Teachers' College in the Guerrero town of Ayotzinapa. (La Jornada, Nov. 28, Nov. 28)

Two volunteers who helped feed Central American migrants passing through Mexico were shot dead on Nov. 23 while talking in their car near the house where they lived in Huehuetoca, México state, according to human rights defenders speaking at a Nov. 26 press conference. The victims were identified as Adrián, a local resident who described himself as a transvestite, and Wilson, a Honduran migrant who was granted a humanitarian visa by the government in November after testifying to the Assistant Attorney General's Office for Special Investigations on Organized Crime (SEIDO). Human rights defenders asked the media not to use the volunteers' last names in order to protect their families.

On Nov. 20 tens of thousands of protesters marched through downtown Mexico City in the fourth National and Global Day of Action for Ayotzinapa, demanding the return of 43 missing students from the Raúl Isidro Burgos Rural Teachers' College, located in Ayotzinapa in the southwestern state of Guerrero. The students were abducted the night of Sept. 26-27 in the Guerrero city of Iguala de la Independencia, apparently in a joint action by municipal police and local drug gangs; three other students were killed in the incident, along with three bystanders. The Nov. 20 demonstration, which also marked the official anniversary of the start of the 1910 Mexican Revolution, coincided with the arrival in the capital of three caravans led by parents of the missing students; the parents had spent a week traveling through different parts of Mexico to increase public awareness about the disappearances.