I have a theory: If he landed on the ground he probably survived. But he would loose some of his belongings on the way down,- clothing, glasses, shoe(s), or other items that would eventually be found.  No such things surfaced.  So.. he landed in a lake or river. (and froze to death). But then the parachute - because of it's size and white/light color would be spotted by divers. Didn't happen.   Ergo: He didn't get his chute open, landed in water and sank with his belongings.  
  Some people went missing, but Melvin Wilson a couple of months before the incident. (Vicki W's father was mentioned, who's he?)
  Then further on my hypothesis: The alias Dan Cooper is not a coincident. He came across the comic somewhere it was sold. So there is a french-canadian OR a francophone european link, and then          Belgium/Brussels most likely. 
  So my question: Have potential canadian citizens (living after 1971 or missing) been looked at?  Have any of the known suspects - Kenny, Weber, Mc Coy etc. a french-canadian connection? Or were any of them at some point stationed in Brussels (Nato HQ) or in France, Luxembourg, Switzerland?  
  A guess:  He is (was) a canadian with local knowledge. Unless Canadian authorities were involved in the investigation, he went under the radar of the US.
  OR:
  He was a belgian citizen that lived for some time in the area before the crime. French was not his mother tongue because they have a really hard time speaking without an accent. But flemish (belgian dutch) is easier to camouflage.