The watchdog said the deaths occurred following an operation in January to crack down on vigilantes in the city of Apatzingan in the heart of the troubled Hot Land region of the state of Michoacan.
Government and church sources have indicated the pope will visit past and current drug war hotspots Ciudad Juarez and Michoacán state, as well as the poverty-stricken state of Chiapas where Central American migrants are facing a government crackdown.
The US-based group Human Rights Watch has highlighted evidence it has gathered suggesting unarmed civilians were killed by federal police in two separate incidents in which a total of 50 people died.
Remember 2000? Fifteen years since the transition to a multi-party democracy, Mexico's PRI machine is back in power and presiding over a fearful, sour midterm vote. President Peña Nieto's party will likely retain control of Congress.
In Ocotlan, Jalisco, locals called the government's raid of a cartel-controlled ranch a "massacre." Authorities hit the airwaves to deny the claims, but troubling inconsistencies hover over the case.
Mexican military and federal forces chased suspects to a ranch, where gunfire erupted that lasted three hours and left 43 dead. The killed suspects are said to be tied to the Jalisco New Generation Cartel.
In internal documents, Pentagon analysts at US Northern Command express concern over cases of security forces killing unarmed civilians in Mexico. The US has sent $2.5 billion to Mexico for its fight against drug cartels.
Former rural police officers were protesting their disbanding and lack of pay when Mexican federal police stormed their encampment and proceeded to execute at least 16 people, according to this special report.
After the missing 43 and the massacre at Tlatlaya, the country is now facing a third likely state-led mass killing in less than a year. A journalist says federal police killed 16 civilians in Apatzingan, Michoacan.
Troops marched into Michoacan in 2006, then federal forces came again in 2014, in response to a growing militia movement. A year after that, violent attacks, extortion, and impunity pervades across the "Hot Land" region.