I'm not expecting answers to these questions but eventually it would be instructive to know if this was a botched abduction and the girls bravely tried to escape, realising they were being taken to a car or a more concealed location. This resulted in the attacker killing them to prevent his identification.
Given DNA advances there is no way now for a rapist to avoid detection unless he ensures that the victim's body is not found. Or no vehicle involved, RA is well within walking distances, no cameras between his house and the bridge, good way to avoid being tracked and leave his phone at another location.
Always bugged me though that the girls seemed to be waiting for someone and that that location was ideal for a predator to cut them off from escape. So some kind of prior internet contact would make sense, the location and crime seems so choreographed. Hence the KK link? Or were LE working so hard to eliminate a defence lawyer throwing him out as an alternative suspect?