Fleeting theory alert: So when we look back at this case, we see a completely shoddy police investigation right? No logs. Didn't secure the scene. Didn't go in the house. Didn't separate witnesses. My thought is that they expected KR to just go away. They present her with the what evidence they had and the fact that it is her against the world and considering she was intoxicated, that she'd just accept a plea and go away.
I do think many of the players just reacted to their own confirmation bias, i.e. the cops must be all telling the truth and KR is a "whackjob." But whatever the case, it is quite obvious that no one thought it was necessary to do any sort of real investigation after finding a dead body on the lawn a cop's home after a late night party.
Poor John. He may never get the justice he deserves. IMO.