DN seems to like to return to scenes. After the latest statements by Port Royal PD, my thoughts are flipping the Delphi scenario around just a bit.
DN indecently exposed himself in a parking lot to two victims on the same day in 2007 in Port Royal, SC.
Per Port Royal PD he returned the very next day.
(Note: this was the case he was arrested 10/3/2007 and convicted for, then appealed and lost the appeal.
http://www.sccourts.org/opinions/displayUnPubOpinion.cfm?caseNo=2010-UP-071)
Then he arouses suspicions of a member of Tim Watkins search party after driving past them more than once in a car with out of state plates, so the searcher snapped a couple photos of him driving by. Was he returning to the scene of a crime he committed (hatchet menacing, murder) and monitoring it?
Which leads me to: what if he was on the high bridge on 2/13 but that wasn't his first day of criminal activity there, it was his 'return to the scene' day?
What if he was there on the weekend, Saturday 2/11 or Sunday 2/12, when there was a likelihood of higher trail traffic. He exposed himself to someone, maybe behaved in a menacing way, and he was close enough they got a good look at him (and vice versa) and they were too scared to report it. (The witness who assisted with the sketch but didn't come forward till months later?) DN doesn't have anywhere to be on Monday 2/13, so as he apparently likes to do he returns to the High Bridge/trails again and this time encounters Libby and Abby. (We could argue he wouldn't know if he'd been reported on 2/11 or 2/12, so it was risky to return on 2/13. But based on Port Royal P.D. facts and possibilities in Colorado, DN has no problems returning to an area and risking running into LE.)
Sources:
http://www.krdo.com/news/teller-county/more-details-unveiled-on-nationss-criminal-past/633133350
http://wane.com/2017/07/17/indiana-police-to-release-new-evidence-in-killing-of-2-teens/