I like this theory...a comment from the article...
“Seriously, I don’t think the guy jumped - I think it was a ruse to make people think he jumped and then he hid on the plane, probably in some maintenance cubby, until things quieted down, then he slipped away with the money. Everyone was ordered into the cabin, then he opened the rear door threw a couple of parachutes out with one bundle of money and then went to his hiding place on the plane. With the hijacking taking place in such close proximity to the Boeing manufacturing plant in Seattle this man most likely worked for Boeing and therefore would know the ins and outs of an airplane and just where to hide without being found. Just my humble theory....”
The pilot and copilot documented D.B. Cooper’s jump time:
“At approximately 7:40 pm the 727 took off with only Cooper, pilot Scott, flight attendant Mucklow, copilot Rataczak, and flight engineer H.E. Anderson aboard.
“The crew soon noticed a subjective change of air pressure, indicating that the aft door was open.
“At approximately 8:13 pm, the aircraft’s tail section sustained a sudden upward movement, significant enough to require trimming to bring the plane back to level flight.”
http://en.wikipedia.org/wiki/D._B._Cooper