Yes, I have considered an accomplice too and I never really considered two and it is really not my theory but I just was thinking what if he was not saying that to them, or even possibly, neither thing to them, maybe not even "down the hill". They also would not have to be accomplices necessarily but someone who was there prior...
I have said it before but I agree with you "guys" just does not fit to me. "Hey guys" does or other words with it perhaps... If he started a sentence with just "guys" or used only that one word with two girls, it is a bit odd to me. I did have a light bulb moment today though and tried to think of all of the people I have known in life would anyone just start out "Guys" to two girls or others and I came up with one person I know that does that, would do that or has done that... And she just happens to be a teacher and a coach and played sports and has been coached... So if it was directed at the girls, I go back to my general instinct that it was someone who deals with kids and uses the term a lot and/or has authority over children.
I am going to read your serial killer link now