I'm familiar with this story, and it's been something that tried to piece together for a while.
Stay with me a bit, and I'll try not to make it a scrawl.
First, it's obvious that Cooper had done his intel work, from knowing where to drop, handle the hostage situation, etc. This man was no idiot.
Add to this the fact that he parachuted out of an air-plane, and I would bet the house on Mr. Cooper being ex-military, and highly trained at that.
His fate is also a lingering question, did he survive the weather conditions once he dropped? Many experts point out that he was too lightly dressed for the cold he would have had to endure, but I'm having a hard time believing he wasn't prepared for that with some thermal clothing under the suit and tie.
We also had a packet of bills discovered from the money he absconded with, this could have been a ruse. I expect that Mr Cooper would have been smart enough to have someone ready to pick him up, and that this wasn't a one man operation, it was two.
In summary, an ex-military type, possibly an officer, that staged and got away with a hijacking. Today's technology wouldn't allow a repeat of that.