Nin, I suspect the attack occurred on Monday afternoon because it was a school holiday. Otherwise the two girls would have been in school. This begs the question often discussed here, was this a pre-planned meeting where the two girls thought they would be meeting someone else other than the killer, or was this a chance meeting? If it was a chance meeting for the two girls, was it also a chance meeting on behalf of the killer, or was he purposefully lying in wait for anyone who happened to show that afternoon and would kill them if the circumstance allowed it?
A decision making tree for each scenario could help keep information that is ambiguous in its meaning from clouding the larger discussion. If the information is just floating around clarity suffers.