On your first point:
There have been countless allegations of police corruption AND federal corruption with law enforcement agencies in doing exactly this, be it anything from politics, to trying to cover for the NCAA college football programs and the various rapes on campuses, etc.
Even away from the corruption angle, there are countless people out there who have testified before they have been threatened by the feds with criminal charges if they say anything during an active investigation - doesn't even have to be political, but the number of people out there claiming this happened on the various federal cases over the years is countless (and I actually do agree with them doing this if there is an investigation ongoing). Way too much smoke out there on a ton of different cases for there not to be fire.
If you really believe point 1, you are super fucking naive.