Ras, you asked, so I will give you my honest opinion. On that note, there are a number of current / former Peace Officers on this board, so maybe they will see this and chime in as well...
1. I can only speak back to 2000 (1993 if you count my time as an MP), but the change is difficult if not impossible to describe here. Mind you, I only have experience to speak of from 3 agencies, all in SE Georgia, but the way we operate now in no way resembles what we did way back then. I'd like to think we have become more professional, educated, trained, and developed. I know I have. But much like chain restaurants, the level of service varies from agency to agency. Some are still stuck in the 90's, and some are so far to the left now that they almost have to ask your permission to arrest you.
2. No. I have some experience here, both as "first on scene", and as an investigator. The initial canvass is critical. Identify everyone who might know anything, or be involved in any way. Coppage 101.
Hope that helped.
Oh..."Best Evidence" refers to the body, which is the best evidence of what happened to JFK. Once you know "what", then you can work on "how". Solid book. If you really want to know what happened, this is a good place to start your quest.
Happy Hunting. When you finish that, we can talk about RFK and MLK. It was a decade of assassinations, and we've been lied to about all 3 of those.