From several things you have posted:
1. Sanchez had NO BUSINESS being involved in this case. He was a childhood friend of Davila. That he is STILL involved tells me volumes.
2. It is apparent to me that Sanchez is running Davila in an undercover operation. I'm HIGHLY suspicious that Sanchez is letting Davila get away with a lot of lawbrealing, just to hide his involvment.
3. I suspect Sanchez is a dirty BP agent. He is in a supervisory position in the ID office. He can spot trouble and warn off his childhood friend.
I don't know how they judge when a person is too close to a case to be involved. I'm still not entirely clear whether it is Rene Sanchez, or Chris Sanchez, that are accused of knowing the guy when he was a child. I know that it was Rene's mother that new Davila's mother, and that it was Rene that reported the shooting, but Rene wasn't the investigator.
Chris was the investigator, he might have known the guy when he was 7 years old? The DHS report indicates that a different investigator tried to call Davilas on the phone, and held the official post-immunity interview; Chris may have been used because Davilas was comfortable with him and Chris spoke spanish, to transport Davilas around. I don't know.
There's no indication that Chris's involvement, or Rene's involvement, caused Compean and Ramos to tell conflicting stories, to shoot an unarmed man in the butt, to cover their tracks, to ask others to cover up the shooting, to fail to report the shooting, or to change their stories over time while talking to investigators (compean; ramos apparently stayed quiet).
Nor is there any indication that either Sanchez testified in court, or that they had anything to do with the testimony of others in court. Chris Sanchez DID have possession of the bullet for a night, but since the defense stipulated that the bullet was Ramos's bullet, that fact has absolutely no bearing on the case.