The problem is that this exists already and doesn't work. The fundamental problem is that "suspect" is based on assumption of guilt first and not on assumption of "innocence" first.
We already have enough evidence that the "haystacks" are far too big. Law enforcement should required very highly trained individuals that have extremely high standards of protecting the citizenry without requiring exceptions to obeying the law. Yet, what we see is LEO's of all description who are self-entitled, above the law and are only concerned about what they want, they kill, they steal, they destroy with the courts (in many cases) just giving them a free pass.
Society at large, doesn't trust them and these non-trusted groups are not interested (on the whole) to change to gain that trust back. So, until they change there is no logical reason for giving them any leeway.
In terms of your exceptional cases, there are laws already on the books that handle this. There is no need for additional specialised law to cover these cases.
The problem of "crime prevention" is that this is not an add-on feature. "Crime prevention" is a fundamental feature of a society that is responsible. Yes, there will be instances of a crime happening and you need to deal with this after the event with the appropriate action. Unfortunately, in today's society, many things that are "crimes" only because a section of society think they should be are treated as more serious than things that are really crimes. So copying a film is more punishable than taking a life. Go on from there.
[edits to correct spelling]