Updated

The apparent execution of a wounded fuel theft suspect by a Mexican soldier caught on video has provided graphic evidence of a long-suspected practice and put the 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, which claimed it provided rare evidence of an extrajudicial execution. But President Enrique Pena Nieto has limited his public comments to saying there should be an investigation.

And it remains unclear how the images will affect public perception of the military's role in combating organized crime as lawmakers debate a law that Pena Nieto has said is needed to give "certainty" to the military in its policing role.