Not to be argumentative, but how the heck would you identify them?
The 20 year old with the freshly plucked eyebrows, with the nondescript earings, accompanied by her grandma with the gray streaks, and bushy eyebrows? Just Saying, this is really a conundrum...
I think the idea would be to look at the records and identify people who would further fit the bill again, connections to the area, criminal records etc. It would not even be that hard, a few days work to compile a list to see if there is anyone worth looking at more closely. We are only talking a few airports within the vicinity that serve Mexico. I'd be surprised if all told there were more than two or three flights that would be applicable. I'd be surprised if this weren't being looked at. Every detail is worth a shot. What if they discovered someone traveling out of sacrifice to Mexico that had previously violent crimes and or sexual criminal history just happened to be traveling to Mexico with an older and younger woman. IMO is a Longshot but one worth looking at.