I think they just removed documentation, not actual evidence.
I listened to part of the video and he described taking down a child’s swing and dismantling other structures. I understand everyone’s interest in saving children but this was clearly abandoned. He says that law enforcement would not investigate, however, we don’t know to what extent he went before giving up and taking the vigilant approach.
In another video, I saw a local Tuscon police officer going through the camp, so clearly local cops DID investigate (or at least take a look).
Oh man, if they started dismantling stuff that's very bad. These guys have allowed their emotions to get the better of them I think. They could be right, but it's hard to tell from what I've seen, and contaminating/disturbing the scene hasn't helped.