The apparent killing of a wounded fuel theft suspect by a Mexican soldier caught on video has provided graphic evidence of a long-suspected practice.
It has also put the country's government in an awkward spot as it tries to pass a security law critics say could shield troops.
Outrage at the surveillance camera video posted by media this week was swift from human rights groups.
They say it provided rare evidence of an extra-judicial execution.
But President Enrique Pena Nieto has limited his public comments to saying there should be an investigation.
It remains unclear how the images will affect public perception of the military's role in combating organised crime as politicians debate a law that Mr Pena Nieto has said is needed to give "certainty" to the military in its policing role.