On the afternoon of November 24, 1971, an unknown man boarded flight 305 from Portland, Oregon, to Seattle, Washington. He sat there and ordered a bourbon and soda, before slipping a note to a flight attendant as she went about her duty, the beginning of one of the strangest unsolved mysteries of the 20th century.

The man had booked his one-way ticket under the name Dan Cooper, which was almost certainly an alias. Dressed smartly in a suit and generally polite, flight attendant Florence Schaffner assumed he – like so many other single men on her flights – was attempting to slip her his number when he passed her that piece of paper.

"Miss, you'd better look at that note," he soon cleared up, "I have a bomb."

Schaffner sat beside him, where he showed her the bomb and explained to her his demands.

“I want $200,000 by 5:00 p.m. In cash. Put in a knapsack. I want two back parachutes and two front parachutes. When we land, I want a fuel truck ready to refuel. No funny stuff or I’ll do the job.”

Schaffner told the pilot the situation. While he conveyed the demands to the ground, she returned to the passengers, and found Cooper sat there, still calm and now wearing sunglasses to go with his full suit. The man's calm demeanor helped to convince the crew and authorities to go along with his demands.

"He appeared to be as rational as someone could be who would do something like that," co-pilot Bill Radaczak later said. "Because he did not appear to be emotional, we felt we could keep the situation in hand if we went along with his requests."

When the plane landed to refuel – the authorities having assembled the required money and parachutes while the plane circled overhead – Cooper released the passengers as he had promised. The Boeing 727 took off once more, this time with only Cooper and four crew members on board, and headed to the new destination of Mexico.

He would never reach that destination. While the crew sat in the cockpit, they noticed a change in air pressure. Cooper – presumably using one of the parachutes he requested – had jumped from the plane, never to be seen again. 

Since the hijacking, there have been many theories about who DB Cooper (as he became known, due to a transcription error by a journalist), much of it based on speculation about various characters. But there is a limited amount of physical evidence, including a tie that Cooper left behind on the aircraft, which was examined by the FBI.

As technology has improved, the tie has been re-examined several times since the hijacking by various investigative teams. Using electron microscopy, a team in 2011 were able to find evidence on the clip-on tie that Cooper could have been a disgruntled ex-employee with a grudge against Boeing.

“One of the most notable particles that we’ve found, that had us the most excited, was titanium metal,” lead scientist Tom Kaye explained at the time. Titanium was a lot rarer in the 1970s, but it was used in Boeing's Super Sonic Transport project, one of the first passenger planes to use the metal.

“In 1971 there was a big upheaval in the titanium industry with the cancelling of the SST project, which happened to be at Boeing, and that laid a lot of people off in the industry. So Cooper could have been part of the fallout."

“Because he wore a tie, we think he was an engineer or manager who went out on the shop floor regularly," Kaye said.

Not all are convinced. Poring over the data from that team, which was commissioned by the FBI, amateur investigator Eric Ulis had a different interpretation. What interested him was three particles of an alloy made of titanium and antimony. This alloy, he believes, was manufactured by Rem-Cru, who operated in  Midland, Pennsylvania at the time.

“I believe that we have identified not only the company where D.B. Cooper came from," Ulis told King 5, "but also the specific division within the company that D.B. Cooper came from."

Ulis, who has a person of interest in mind, is now suing the FBI in an attempt to get his hands on samples of the tie. Though they have already tested the tie for DNA, he believes DNA could be obtained by swabbing the tie knot's metal spindle, which could then be run through a DNA database and perhaps solve the mystery once and for all.

[H/T: Popular Mechanics]

An earlier version of this article was published in July 2022.