More likely they are regular cops participating in some joint task force. There are more state, county, and local police agencies in this country than there are FBI Special Agents.

I see a lot of police bodycam videos on YouTube of cops stopping drug traffickers for bullshit reasons (5 over speed limit on highway, crossing the line, following too closely) and it's usually a state or county cop that's on a federal task force or they'll have a "civilian ride along" in the car that gets way more involved than any civilian would ever be. They aren't actually an employee of the FBI but they have credentials from the FBI due to their task force job, it gives them access to FBI databases and bulletins while they still maintain their normal police job.

It's really bizarre to watch those videos because they are very routine. They stop the person for marginal lawbreaking, ask them to step out and sit in the front of their cruiser, then the traffic violations turn into warnings, cop makes basic small talk while writing warning and pretty much ignores everything suspect says, cop asks about any contraband in the car and asks to search, suspect usually (stupidly) agrees to search, cops pretty much instantly find the drugs. And if the suspect says no to the search, the K9 unit is already pulling up behind them because they were called before the cop ever turned on their lights and siren.

It's incredibly obvious these are pretextual stops. There is definitely a national program tracking license plates because there's no reasonable explanation for cops getting this lucky on pulling over random people that are driving completely unremarkable.

I'm pretty sure that's how they caught that megachurch pastor smuggling drugs for the cartel, they look for travel patterns for license plates and especially look at rental car registrations. You can't pull over every car but you can definitely look for cars making repeated trips, especially those that are made to known trafficking cities.

I had a friend from highschool that got pretty involved with his mom with drug trafficking. They caught him at some Indian reservation that overlaps upstate NY and Canada. The arrest affidavit states the cops saw a car parked for a couple hours at a casino and then followed the car to the border of the Indian reservation. Then they waited for the car to leave and then pulled him over for crossing a line. Of course they found significant ketamine in the car. The cops already knew who they were looking for because a car parked at a casino for a couple hours is not suspicious and definitely not suspicious enough to follow.

If that ever happens to you then document on a Blockchain that you have first-hand knowledge that someone has committed a crime against you, specifically 18 U.S. Code § 242. By not reporting a crime like that you could leave your fellow Americans exposed to a criminal by leaving that criminal undocumented. But, be very careful as in doing so you are liable for your spoken or written utterances.

  18 U.S. Code § 242 - Deprivation of rights under color of law 

  Whoever, under color of any law, statute, ordinance, regulation, or custom, willfully subjects any person in any State, Territory, Commonwealth, Possession, or District to the deprivation of any rights, privileges, or immunities secured or protected by the Constitution or laws of the United States, or to different punishments, pains, or penalties, on account of such person being an alien, or by reason of his color, or race, than are prescribed for the punishment of citizens, shall be fined under this title or imprisoned not more than one year, or both [..]

  https://www.law.cornell.edu/uscode/text/18/242