IIRC (MOO), Libby had been asking multiple times the past week to get a ride from her sister to the High Bridge, seemingly intent on getting over there for some reason - not so sure about spur of the moment...Although the trip was to the bridge was apparently very spur of the moment (and not even their first choice outing). I’ve been convinced KK was involved for some time but it does seem possible RA was trolling the bridge on the offchance he would run into a potential victim/or victims. Was it a school holiday? The PCA alludes to other young witnesses on the trail.
If he was trolling the bridge on the possibility he'd encounter potential victim(s), he apparently bypassed the first (3 female juveniles) vulnerable individuals he crossed paths with near the Freedom Bridge. Perhaps he knew that location was insufficient or didn't think he could handle 3 people, and would take his offchances on others elsewhere - or of course could've known that A & L were scheduled at the South End of High Bridge.
Yes, it was sort of a school holiday - for likely Delphi students only. Long answer is that Indiana in 2017 required 180 days of in-person instruction. As it snows, sometimes a lot, in Indiana most school corporations build around 5 snow days into the school calendar (scheduling say 185 days) so that the school year doesn't have to extend into the summer to achieve the 180 days if snow-related school cancellations accumulate in the winter. If the winter progresses without very many cancellations, school corps normally release days off one-by-one in Feb/March/April, typically on Mondays/Fridays so that they don't have to give a whole extra week off in May/June. This Feb 13, 2017 was originally scheduled as a school day but it was likely announced at the previous monthly Delphi school board meeting that 2/13 would instead be a day off since few snow-cancellation days had occurred so far. Interestingly, if a murder/significant meetup were pre-planned far in advance, the following Monday 2/20/17 as President's Day would've been a much more likely date chosen, being a much more universal school holiday on the calendar as a day off from the beginning and for almost all school districts around and including Delphi. As the timing appears to have worked out, even a school day in Delphi Jr. High dismissed at 3:15 thus these events that happened from 2:13 to 3:57 only provided an extra hour over what any given day might've allowed.