Why do they think that none of the $200,000 from the 1971 crime never made it into circulation? Well, the FBI believes that Cooper died when he jumped out of the plane. They don't think he even opened the parachute. Of course, this is purely speculation on the FBI's part. Therefore, if D.B. Cooper died, then he didn't spend any of the money.
At the time, several rewards were offered for returning any of the money, and the serial numbers of all the $20 bills were distributed to banks. In his 1985 book, "D.B. Cooper, What Really Happened," Max Gunther wrote:
"Bank people feel in general that their chances of participating in any meaningful way in such rewards are slim. If an alert teller or bookkeeping clerk spots a listed bill, that is typically the first minor step in an investigation. The bill may have changed hands many times since it was originally spent by the criminal being sought. Tracking the bill back to that criminal would involve a long chain of people, most of whom will feel they have a greater claim on the reward than the teller who first spotted the bill. In most cases the biggest share of the reward--if not all of it--goes to the detective or witness who makes the final connections leading to the arrest. The teller, if lucky, gets ten bucks and a letter of official gratitude. More often, the teller gets forgotten."
It's doubtful that any serious attempt was made to spot any of the bills.
Now, Kenneth Christiansen, who was employed by Northwest as a flight attendant, purchased a house with cash about a year after D.B. Cooper carried out his daring crime. Also, his lifestyle was seemingly beyond the means of most Northwest employees.
I recently talked with Bill Rataczak, the co-pilot of Flight 305, the Boeing 727 that Cooper hijacked. He told me that Cooper insisted that the wing flaps be tilted 15 degrees, to slow the plane down. "He knew that airplane," he said. "A flight attendant wouldn't know to do that." I reminded him that Christiansen was a Northwest mechanic before he became a flight attendant. He said that he didn't know that. He also didn't know that Christiansen was a former paratrooper.
The FBI asked Sherlock Investigations to submit DNA evidence from Kenneth Christiansen. We did about nine months ago. It's probably in a box with all the other evidence from the case, in the basement of the FBI office in Seattle.