My first thought when I heard that MS13 was heading to the border to "teach the gringos a lesson".
Why bother tangling with armed men when they could just shoot up a group of "migrants", a shooting which the open-borders lobby and illegal alien symps would love to pin on the "drunkard" "racist" MMP. The MSM would follow along as they always do without scratching beneath the surface to see who is really responsible or who stands to benefit from such an incident and the negative exposure aimed at the MMP.
There have already been, as mentioned in another post on a related thread, television spots running in Mexico showing "white" men shooting down a schoolaged Mexican girl trying to get across the border.
The 'zetas' sound like they are just the sort to pull off something like this.
Right out of EFAD.