Some of the 'bad guys' look to have blindfolds on. And some of the bodies postures suggest that the hands may have been tied behind their backs prior to death and untied before the photos.
My guess is that the Mexican army personnel 'stiched' some captured 'bad guys'.
Execution is a surefire way to prevent the enemy from reentering the fight at a later time.
And they call themselves the "first world"....go around the world with their "united nations" telling everyone what politics to install in their own countries. FOOEY