I'm finally getting around to responding to a Skribit question:
An investigator seizes evidence illegally, do you decline to press charges or go forward?
I quote the question as asked because I don't want to be accused of not answering it, or misrepresenting the question. I say that because it's a little ambiguous so I have to make some assumptions.
Firs, the word "investigator." When I hear that word I think of Mike, the former cop who is the DA investigator assigned to my court. But I'm going to assume you mean "policeman."
Second, when you say he seized evidence "illegally" I'm going to assume he did so in violation of someone's Constitutional rights, as opposed to, say, breaking into someone's car or home and rummaging through their stuff (some might say the difference is negligible!).
Third, it's not 100 percent clear whether in your hypo I'm pressing charges against the investigator or the person from whom the evidence was taken. I shall assume the latter.
The other problem with the question is that it assumes the evidence was seized illegally. It's a problem simply because it renders the question fairly easy: if it's blindingly obvious the evidence was seized in violation of someone's Fourth Amendment rights I will acknowledge that fact and, almost certainly, not go ahead with the prosecution.
The most common situation, though, arises when it's not completely clear that the seizure was illegal. That's when the defense lawyer files his motion to suppress and we have a hearing in front of the judge. Now, sometimes one side or the other will push for that hearing even when the answer is pretty clear, one way or the other. That's because they might want the issue to go up on appeal so a higher court can write an opinion and make that area of the law more clear.
I should add that I don't see blatant violations very often, thankfully. Hardly ever, in fact. A year ago the law changed with regard to searching vehicles after an arrest and for a while the cops were not completely au fait with the new rules but they caught up fast. And until they did I didn't wait for the defense lawyer to point out what was now a violation of the Constitution.
Hope that answers the question, if not, let me know.