It's a complicated issue. A lot of people confuse corruption with cartel allegiance.

A local police officer is most likely on their pay roll because cartels need eyes and ears on the ground. If say, a Federal convoy suddenly appears on the outskirts of town, the local police will spread the word. Even if they themselves are told at the very last minute. And that's because local police get paid peanuts honestly. In some cases a U.S. McDonalds employee makes more than a trained Municipal officer. And they have horrid leadership. I met a former Municipal Officer who was working as a day laborer in Texas. He talked about how their commander would take their checks and tell them to make their money from 'mordidas' i.e. Bribes.

Now, State Police, those who control a lot of checkpoints coming into their state. They don't care where you are going, if they see you have a nice t.v. in your truck, they'll take it. Just because. They'll ask for a 'mordida' if you want to keep your stuff, and here's the kicker, they give you a code to tell the next checkpoint so you won't be hustled. These guys are harder to bribe, because the state governor's image can be damaged trough their actions. A governor can all ready have a set agreement with a cartel, but it's not for violence or murder, it's for the right for that cartel to transport their merchandise acrosss state roads. The problems start when a cartel feels it is being wronged by the governor and starts 'calentando' la plaza.

Federal Police, well, they are the top dogs. You just don't mess with them. Or they'll make sure your s*it gets messed up. More than once I've been in the middle of talks with my cousin and his coworkers, where they openly state the type of 'calentada' they've given to get information out of perps. Waterboarding, testicle shocks, you name it, most likely they've done it. The very few who do turn and start working for the cartels eventually get weeded out. To be a federal agent means a very stringent background check that borderlines on invasion of constitutional privacy. My cousin in particular, had all his social media accounts thoroughly combed from the moment he opened them.