I wonder if Cooper had some accomplices that helped with this? I am new to this forum and I watched the special on the history channel on DB Cooper and with some things making the news shortly after has got me interested in this case....
Welcome to the Forum, DC.
There is no definitive evidence to say there were any accomplices, but theories abound - and in two categories. One is help in performing the skyjacking. Lots of people have posed flight crew as accomplices, but I see no compelling reason to entertain that scenario.
A related option is the idea that equipment and supplies might have been placed in the overhead bins. Again, I see that as a long shot.
For me the most compelling speculation is: did DB Cooper have a getaway team? I say this idea has some merit because I feel Cooper had unique capabilities - he had advanced knowledge of how to jump from a 727. In fact, his knowledge that a 727 could be flown with the aft stairs down was top-secret information.
So, if Cooper had access to top-secret info he might have also had access to a network of top-secret operatives, such as commandos who might have been an extraction team - well-equipped and ready to rock and roll.
I encourage you to read my book where these possibilities are examined in detail. My online news magazine, The Mountain News-WA, also has many DB Cooper postings and is free to read.
In addition, I recommend Geoffrey Gray's SKYJACK, as he describes at least one alleged member of a Cooper getaway team, a fellow named "Jake.".
A warning, though. Much of what is written above is considered controversial, and is strongly mocked here.
Lastly, I don't buy the Reno jump theory at all, and I believe it seriously detracts from the "Expedition Unknown" show. Along those lines I have encouraged the Travel Channel and EU to re-enact the Cooper jump: at night, in the rain, in November, using a round canopy, over the woods in Ariel, wearing a thin business suit.