Three Amigos Summit the perfect time to hold President Enrique Peña Nieto accountable for human rights violations.

This time it is impossible to look the other way. The Mexican government is normally adept at managing public opinion so the responsibility for the violence and human rights violations ripping apart the country falls on the shoulders of local officials or organized crime groups. But on June 19th that narrative was broken under the heavy weight of the facts.

The press originally reported a “clash between teachers and police” in the town of Nochixtlán in the southern state of Oaxaca. The authorities claimed their agents were unarmed and the protesters had fired on them first. The new U.S. Ambassador to Mexico, Roberta Jacobson, was carefully neutral in her first public evaluation of the incident, stating simply that she “lamented the loss of human lives.”

But during the ensuing days the awful truth has trickled out. Thanks to the reports of journalists on the scene, the Mexican government has been forced to accept that the police were in fact heavily armed. And the evidence now points to the commission of a brutal massacre by federal forces against peaceful protesters. These forces are under the command of Mexico´s President Enrique Peña Nieto and receive significant funding from the United States government under the Merida Initiative.

It all began when a group of rural, elementary school teachers closed a highway that runs through the small, mostly indigenous town of Nochixtlán. They were protesting the government´s neo-liberal education reforms and in favour of the release of two top teacher union activists, who had been taken as political prisoners a week earlier.

Instead of negotiating with the protesters, or using limited force to liberate the highway, the federal government decided to violently quash the uprising. Peña Nieto sent hundreds of masked police officers armed with high-powered automatic rifles and tear gas to run off the protesters. In response, the surrounding communities called for reinforcements. Church bells ran, a form of SOS call to the surrounding villages, and hundreds of residents appeared on the scene in support of the peaceful teachers. Although some of the reinforcements did throw rocks and launch fire crackers at the riot police, none of the protesters were armed nor were the lives of law enforcement officials put at risk.

The police acted with desperate vengeance. According to eyewitness accounts, plain clothes police first set fire to buses and cars in order to create the impression of chaos and thereby “justify” the upcoming brutal attack. The uniformed agents then opened fire on the innocent crowd. Nine protesters were killed, dozens wounded and many others arbitrarily arrested by law enforcement, who grabbed anyone they could get their hands on. Amid the chaos, the police even interrupted a family funeral taking place in the town cemetery to haul off to jail dozens of the attendees who had no connection to the protests.

The federal police also indiscriminately launched dozens of tear gas canisters from land and air during the assault. One of them landed in the patio of a health clinic, which was attending to the wounded, forcing it to close down and thereby putting numerous lives at risk.

Such attacks by Mexico´s highly militarized federal police on the civilian population are not rare. Excessive use of force has become commonplace in recent years, especially since the beginning of the Peña Nieto administration in December of 2012. Civilian deaths are normally presented as the result of frontal combat with narcotraffickers or “criminals.” In fact, local and international government and non-governmental organizations have unveiled the systematic abuse of human rights by security forces in Mexico.

But this time the violation of human rights is particularly glaring. The victims cannot be presented as “criminals” even by the most creative imagination. They were all peaceful protesters, teachers and community members, standing up for their rights. In response, the government turned a sleepy, rural town into a war zone.

Mexico has erupted in protest. Teachers have taken to the streets throughout the country, even in regions such as Monterrey where such activism is rare. Tens of thousands of students and doctors have also mobilized in solidarity. The indigenous communities of Oaxaca have taken action and highways remain blocked throughout the state. This Sunday there was an enormous protest march in Mexico City organized by the principal opposition party, Morena. The international solidarity movement, in Argentina, Spain, France, England, Canada and the United States has also jumped into action. Both the National Human Rights Commission and the United Nations Human Rights Commission have initiated investigations of the attack.