I rather object to "renegade Mexican troops". They're likely not renegade at all. There is no such thing as a lack of knowledge on the part of officers. When guns are involved, knowledge means at least tacit approval, probably gained via mordida from the local narcotrafficante.
In some areas, the marijuana is grown under the protection and supervision of members of the military.
How do I come to believe this? 23 years on the border. Chit-chat with Border Patrol guys and the occasional knowlegeable LEO. Chit-chat "gossip" with folks who ramble back and forth across the border, sometimes living for a while in Mexico.
There are few secrets. It's just that Washington VIPs and the Sean Hannity types don't hang out, drink beer and talk to the locals who've been here for years.
Example: If you read Joaquin Jackson's book, "One Ranger", he speaks of his disbelief that Presidio County Rick Thompson was dirty. He'd known Rick for some three or four years at the time of the arrest for a metric ton of cocaine. The folks down here along the river had known Rick was dirty for over ten years before Joaquin ever met him...
Art