Mexican authorities Wednesday arrested six federal police officers over their alleged involvement in a 2015 massacre in which 16 people were killed in the western state of Michoacan.
"The six people were arrested with full respect for their human rights, without violence or the involvement of third parties, to be made available to the judge who requested them," the attorney general said in a statement.
The officers were arrested inside federal police facilities.
On January 6, 2015, at least 16 people were killed and several others wounded when federal police allegedly shot at members and supporters of civilian self-defense militias who were demonstrating at the city hall in Apatzingan, Michoacan.
At the time, the government of then-president Enrique Pena Nieto said the members of the self-defense groups had died in the crossfire.
However, a journalistic investigation revealed that the federal police had killed unarmed protesters in cold blood.
Michoacan is a flash-point in the violent organized-crime wars that have swept Mexico in recent years, leading to the rise of self-defense groups six years ago and the deployment of soldiers to the state in 2014.
On August 8 this year, 19 bodies were found in a turf war between drug gangs in the city of Uruapan in Michoacan.
The government first deployed the army to fight criminal gangs at the end of 2006 -- a strategy that critics say has only led to an escalation in the grisly violence.
Since then more than 250,000 murders have been recorded, according to official figures, although it is not detailed how many are linked to the fight against crime.