Alright, strap in. It's outlandish theory time.
First, a possible rational explanation for where we are now:
WHAT IF at the time of the initial investigation LE gathered all surrounding cell tower data; and
WHAT IF DNA only recently led them via familial/genealogy to RA; and
WHAT IF they went back to those old phone records with RA's phone info; and
WHAT IF that's what led them to the river search (ok, we found THIS DNA holder in the system, he was near the bridge that day, and this is where he went after, and stopped for a while here)...
This would explain a lot of current situation without involving KK at all.
And here's where it gets weird.
What if the girls were smarter than most people give them credit for, KNEW they were being catfished, and were catfishing multiple creeps online themselves? Including both KK and RA, completely separately. RA meeting them and realizing his exposure could certainly explain how a boring 45-year-old pool-playing CVS employee suddenly becomes a double-murderer.