"My thought/theory on this is that the networks probably use questionable 'evidence' on stories pretty frequently, as a normal way of doing business."
For part of my time in the military I got to read raw intel feeds every day.
As a result, I am convinced that the Networks--and the major newspapers and wire services--lie constantly.
I'm defining "lie" as acting with the malicious intent to deceive. That can take the form of omission, distortion, selective reporting, or outright fabrication.
For instance, I happen to know that some of the anti-Marcos riots in Manila were out and out fabrications. I don't know when the media started inventing stuff, but they've been doing it at least since the Marcos years.
They didn't bother to make it a good forgery because they are just so used to getting away with it. They're just not accustomed to being vulnerable to being caught.
What you describe from your own experiences is consistent with my suspicions. If the public could ever grasp just how much the media fabricate and lie....