DA's have to walk a tightrope, because if they push too hard in an investigation on a cop, they now find the well of police cooperation drying up on them. It's worse for their career to undermine their own ability to get convictions than it is to take on a cop here or there (I feel like the equation changes when you can make a career move like uncovering department-wide corruption).
I agree with you that if you have a different district/office handling this sort of stuff. But it always comes down to Who's Watching the Watchmen. Checks and balances are hard AF.
When a police officer does face charges, uniformed cops will show up en masse as a "show of solidarity" with the defendant but in reality they're trying to intimidate and influence the jury.
This is easy to control; while trials are required to be public, there is no reason a jurisdiction could not prohibit law enforcement officers wearing a uniform in court unless present in an official law enforcement capacity (e.g., acting as a bailiff.)
It's not so easy to control because judges have to be re-elected or aspire to sit on higher benches and having police unions oppose you can make that more difficult.
There's a reason why there are more former prosecutors on the bench than former defense attorneys.
Judges don't make laws (well, at least, they aren't the ones I'm talking about with a jurisdiction-wide, state or federal, prohibition.)
Now, if you want to say that it's not easy to control because legislators and ultimately the electorate are biased toward and support this kind of police intimidation, that may be the case (though that's exactly saying it's not easy to solve because we, as a society, actively desire the status quo. It's easy to solve, it's hard to convince people it should be solved, which has always been the problem with civil liberties.)
Point of order: There's more former prosecutors on the bench than defense attorneys for a myriad of reasons, including financial (public service, bribes excluded, doesn't pay as well) and personal (there are honorable defense lawyers who believe the system is corrupt and want to make sure it doesn't win when it shouldn't).
The fact that they've pissed off the cops may or may not factor into it. Not saying you're wrong, just that it's not quite THAT simple.
Well now we're getting to the real issue with any of this stuff. It's not a great career move for a politician to make moves against the police unions, so trying to get more oversight laws is pretty hard. The unions are strong, their supporters are many, and who in their right mind would want to fight "law and order" that the cops represent.
That is exactly why a special prosecutor should always be appointed and the special prosecutor should always be someone who would not directly work with any police organization connected to the case.
There is an inherent conflict of interest in having the person responsible for investigating crimes be someone who needs to work closely with the people and organizations who allegedly committed the crimes.
I agree with you that if you have a different district/office handling this sort of stuff. But it always comes down to Who's Watching the Watchmen. Checks and balances are hard AF.