I've always believed that the Killer was cunning and left little if anything to chance. He must have known the area very well and I believe planned the attacks to allow him a number of escape routes. Save the generally accepted sightings of him, if indeed they were of him, his meticulous planning certainly paid off. If the victims went willingly to their slaughter, which apparently they did, then he must have been know to them and was trusted or his 'appearance' made him, in their minds, trustworthy. I think the killer will be identified, at some point, and the puzzle perhaps won't be as hard as we've imagined.