I remember listening to the news dispatches on the hijacking as the story unfolded in the late evening Eastern Time. I was in college, years before I flew the 727.
Some of the FBI interviews are on this page:
https://true.ink/story/d-b-cooper-fbi-files-released/
Also, some of the Bureau's Freedom of Information Act releases are published here:
https://vault.fbi.gov/D-B-Cooper%20
Looking over the FBI files, the flight engineer Bill Rataczak, listed in the FBI interview as the 'third officer', seem to think that the hijacker was knowledgeable about aircraft and in particular the 727. He also shared the impression that the hijack was premeditated and well planned.
It turns out that the $200,000 came from a $250,000 stash thoughtfully set aside for ransom money by the Seattle-First National Bank and the used bills had been microfilmed well in advance. Did Cooper somehow know that this $200,000 was available on short notice after hours? But not know that the bills had recorded serial numbers?
The hijacker seemed to be impatient about a refueling delay at Sea Tac blamed on a vapor lock in one of the trucks. When told they would still need to file a flight plan, he said that they could do it in the air, perhaps he had some type of flying experience.
Once the plane was refueled and the pax and two stewardesses let off at Sea Tac, they took off again, ostensibly for Mexico but actually planned for Reno, maybe to refuel.
Cooper wanted to take off with the aft stairs down. When advised that the plane couldn't rotate in that configuration he initially planned to have the onboard stewardess, Tina Mucklow, lower the stairs for him once airborne. Later, he decided to lower the stairs himself and Ms. Mucklow went up to the cockpit for the remainder of the flight.
They were doing 170 knots indicated with stairs and gear down and flaps 15 at 10,000 feet or below according to information in the FBI files. Ground speed, true airspeed and miles per hour numbers seem to be mixed into some of the media accounts.
The crew 'felt an oscillation' somewhere near Portland but continued to Reno seemingly not sure if the hijacker was still aboard. They told the rider over the interphone or PA that the stairs needed to be raised for landing to avoid damage but got no response.
They landed at Reno dragging the stairs and a search found that the passenger was no longer onboard.
I always thought that the story about the SR-71 joining the search for D.B. Cooper was probably urban legend but one of the documents indicates that five passes were indeed made by the SR but nothing was photographed due to cloud cover.
There was a 'fake news' D.B. Cooper interview story picked up in 1972 by several media outlets including
Newsweek and the
LA Times. Someone calling himself Seth Thomas supposedly set up a meeting between Cooper and a reporter for a new weekly publication named
LA. Much of the material in the published 'interview' seems to me to come from the FBI interview documents, I wonder if a 'journalist' was leaked copies to create this apparent media hoax of the perp's survival?
Later the story was debunked and it turns out that the ersatz interviewee was a con-man who received $30,000 and was already in jail before the first installment of the story ran. The reporter turned out to be a guy named Karl Fleming who, predictably, insisted that he did nothing to mislead the readers. When confronted with the, uh, inaccuracies he insisted that the series was an adventure chronicle, as much about him as about D.B. Cooper.
These questionable claims about the hijacking still pop up in print and in TV 'documentaries' but the FBI has officially put the case on ice:
The FBI says it is ending its 45-year pursuit of D.B. Cooper and giving up any real hope of closing the case file on the nation’s only unsolved hijacking. But don’t think the legend — and the quest for Cooper — won’t live on.
The bureau announced Tuesday that it was “redirecting resources” that had been allocated to the investigation into the Thanksgiving Eve 1971 hijacking of a Seattle-bound Boeing 727 that ended when a tall, dark-complexioned man who had identified himself as “D.B. Cooper” parachuted into the pitch dark Northwest night sky with a satchel containing $200,000 in cash. He was never seen again.
The bureau said the case, dubbed NORJAK, has been active since, becoming one of the agency’s “longest and most exhaustive investigations.”
FBI no longer looking for D.B. Cooper | The Seattle Times