I wish to add my sincere condolences to Chelsea's friends and family. She reminds me so much of my best friend in high school, and her death was especially sad for me to where I needed to take a few days away from WS - I have had nightmares the last few nights about what may have happened to her. I can't imagine what her family must be going through, and suggest they maybe scroll past the rest of my post here.
I wanted to offer my wild speculation on how things may have went down now that I can type a coherent thought on this case.
Motive: I agree with roses that this was the work of a group and it was for "ritualistic" reasons, if not so much satanic as in perpetrating something they idealize, fantasize about or think would be 'rad' to experience. I see evidence of this ideation and disconnection with reality all over SM of individuals connected to the bands and to CB. I think back to my teenage days and the kind of guys I knew in high school who were guys in the emo band* and the 'fanboy' type younger kids that would do anything they said.
Opportunity: I think Chelsea was probably drugged or if she went willingly, she was lured by one of those band guys and his minions(including HB) to go 'hang out'. I think she would have jumped at the chance to get a band member's attention, or to go have fun with them (especially if she had been rufied or offered a ride or place to crash), as she seemed very 'starstruck' by the bands in this scene. HB and his friends, to me, seem like pawns with just enough dysfunction to go along with a nefarious plan such as a gang rape. I am not sure if murder was a plan everyone shared, but I do think more than one person was present when it happened, and it may have even been a dare or a situation where the weakest person was made to do it to ensure he never tattles on everyone. I think it is possible HB is the least guilty and, if involved, may be the one that flips first as he has already tried to tell the police something. He is also the least creepy and disturbed of the "group" IMO.
Clothing: It seems obvious to me why she was found unclothed, and I won't go into detail on my speculation there, but the comment about evidence at the scene pointing to homicide does make me think they found blood in the soil or that a murder weapon was found (ie rock, etc)
How the two sites are connected: When I was a kid, we walked the train tracks near my home a lot and became familiar stomping grounds. They were remote, mostly untravelled, and probably had an unconscious 'hard' magnetism of where you go when you're a young derelict, especially when a bridge was involved (excellent drinking and graffiti spot). I see this as a bunch of dope fiend kids* being really stupid and taking something they are not experienced in too far, and dealing with it in a very messy way, hence the found clothing (the state of which we were never told, so it could be partially burned or had been inside or under something) and the short distance to the dump site. I do think something bad happened at the industrial site - my thought is that LE is pretty sure she was killed in the woods because of the evidence (rock, blood etc) so the rape (and I am positive there was one) probably occurred at the industrial site and CB was taken to the dump site and 'finished off'. Thankfully I don't believe she was conscious at that point.
May justice be swift.
*(for anyone new or not following closely, I am referring to one of the other party bands, not BM's)