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 what do we have in the way of physical evidence?

The tie

Physical evidence is scant to say the least, but Cooper did leave his tie behind on the aircraft. 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.

The money

In 1980, a boy vacationing at the Columbia River with his family found three packets of Cooper's ransom money as he raked the river bank in order to build a fire. It was a good lead, but attempts to analyze the money would only make the mystery weirder.

The bundle was weathered and largely disintegrated, with geologists concluding it had been weathered by the river as it floated along it, rather than being deliberately buried. The location of the cash discounted previous theories on Cooper's drop zone, unless the cash had found some method of swimming its way upstream. What was weirder, however, was that 10 bills were missing from one of the packets, as though they had been taken before the packet was resealed. And it doesn't stop there.

Analysis in 2020 showed further nonsensical problems. A team analyzed the money and found tiny deposits of algae.

“The diatoms that we found [on the Cooper money] are a spring species," amateur scientist Tom Kaye – who published a paper on the findings – told King 5. "They bloom in the spring. They do not bloom in November when Cooper jumped."

The money made its way into the river, according to the analysis, months after the hijacking. 

We're still not done, however, as another analysis of the notes and the rubber band suggested that they would have had to have washed up on the shore within a couple of years, otherwise the bands would have deteriorated and broken apart. This doesn't fit with geological evidence, which suggested the notes must have arrived on the bank after a dredging of the river in 1974.

Regrettably, other than DNA taken from the tie which may or may not belong to Cooper himself, other physical evidence from the case is non-existent. Despite this, there are many convincing theories as to who he might be, and whether or not he survived the jump.