Ah, here's some more opinion. I originally thought "down the hill" was a directive. Possibly it was not. It could have been the completion of a sentence, such as "so and so is waiting for you down the hill", or "guys, we've decided to all meet, down the hill".
I'm of the opinion there is no hat on the BG, he's got light brown hair, with a hoodie up against the back of his head, that he merely directed the girls, that he was involved in plotting their murder, but he did not necessarily participate in the actual act of murder. I opine that there was a second killer, the 'new sketch guy', who did the murders and escaped through the cemetary.
These girls had to have been murdered swiftly, or rendered unable to speak/scream, right off the bat. What 8th grade girl wouldn't scream? Were the killers known to them....presenting a level of comfort? Or were they instantly rendered unconcious/murdered, even before crossing the stream?
BG walked out early, being dry head to toe, having never crossed the creek, picked up the car at the abandoned building, drove to the cemetary, picked up the 'new sketch guy' and they booked it out of there.
It was a crime of anger and/or self preservation.
All opinion, of course