I know this was covered before but...

The DEA is not a subsidiary of the NYPD. Local police can investigate all they want but have no jurisdiction over Stansfield or his crew who works for some bureaucrat in Washington, D.C., who probably doesn't even want to know about it unless he has to explain it to a member of Congress. Someone would have to drag them into federal court. Even if they did so, the court would probably let them go free, and it would take years not weeks.

Besson is basing his use of the DEA on real Federal crimes under investigation in the U.S. Congress in 1993. The attack on Mathilda's family combines two real incidents. At Ruby Ridge, a Federal sharpshooter killed a Mother with a baby in her arms and a young boy running away from the attack. In another incident, Feds shot a man repeatedly after he was down (Donald Carlson). In both cases, years later, the feds lost in court but still got away free with no jail time. The team leader responsible at Ruby Ridge described the family they pursued as scum, and claimed we're just "doing our job."

Stansfield tells his flunky to say the same thing to the cops when they show up. In many of the real tragedies documented in 1993, the involvement of local cops, who do indeed answer to local citizens through local government, was the only thing that prevented worse tragedies.