On November 24, 1971, a man perpetrated an incredible crime that still has law-enforcement officials puzzled. 
 
The man, who went by the name D.B. Cooper, boarded Northwest Airlines Flight 305, flying from Portland, Oregon, to Seattle, Washington. After the plane took off, Cooper told flight attendants his briefcase had a bomb in it. The plane, crew, and 36 passengers were hijacked.
 
Cooper requested the plane land in Seattle, where he was to receive $200,000 and a parachute. The airline complied with his demands. After Cooper received his ransom, he ordered the plane to fly slowly and at a low altitude toward Mexico. 
 
Then, somewhere over the forests of the Pacific Northwest, Cooper jumped into the ink-black night, never to be seen again. 
 
The only evidence of the crime was discovered in 1980, when a boy found $5,800 of the ransom money on a sandbar in the middle of the Columbia River. 
 
Though the FBI investigation into the crime is still open, the agency is reluctant to spend resources on a decades-old mystery. So today, “citizen sleuths” with electron microscopes are trying to crack the case.
 
Citizen Sleuths
 
The sleuths began their investigation in 2007, when FBI Seattle Special Agent Larry Carr decided to release information about the crime to the public. 
 
Tom Kaye was on the case. Kaye is not a detective or forensic investigator, however. He’s a paleontologist and associate researcher at the Burke Museum of Natural History and Culture in Seattle. Kaye’s team of citizen sleuths included metallurgist Alan Stone and scientific illustrator Carol Abraczinskas.
 
The key tool that Kaye and his team employed was an electron microscope, which uses electrons to create a higher magnification than a regular microscope. Electron microscopes had never been used to examine physical evidence from the Cooper case. 
 
“In 1971, when Cooper jumped out of the airplane, the FBI didn’t even have an electron microscope,” Kaye says.
 
Kaye and his team used electron microscopy to analyze the money found on the sandbar. Since its discovery, the money had turned black. 
 
“There was a debate about whether or not the money had been buried there since day one,” Kaye says. “Or had the money been tumbling down the river for four or five years and then got washed up on the beach by a dredge?”
 
When Kaye looked at the bills with his electron microscope, he discovered something surprising. 
 
“We started investigating the black coloration of the bills, and the electron microscope told us it was made of silver,” he says. “This is very unusual to find silver on a bill like that.”
 
But the silver lining turned out to be a dead end for the citizen sleuths. 
 
“At the end of the investigation, what we found was the FBI used silver chloride to look for fingerprints on the bill,” Kaye says.
 
The FBI was impressed with the work of Kaye and his team, however.
 
So the agency allowed the citizen sleuths to examine a tie, found on the hijacked plane, that most likely belonged to the criminal. Kaye says the tie had been in an FBI office for 40 years.  
 
“What we were looking for was pollen, because pollen is everywhere,” he says. “The tie is the most ideal thing for him to leave on a plane, because you don’t wash a tie. So we knew that the tie had accumulated particles from everywhere he had been. If we could find pollen on his tie, depending on what pollen we found it could tell us what part of the country he was from.”
 
Once again, Kaye and his team used the electron microscope. Once again, they found something surprising. 
 
“What usually happens in these cases is that you find out the unexpected,” Kaye says. “We found these metal particles on the tie, and one or two of them ended up being titanium, which is very unusual because titanium was not very popular in ’71. And it’s not the type of thing that would have gotten on the tie since 1971 in the FBI lock-up.”
 
Titanium was used in the aircraft industry at the time, and the discovery led Kaye and his team to think that D.B. Cooper may have worked somewhere where aircraft were built. But aircraft were built with titanium alloys, and the team had concluded that the substance on the tie was pure titanium. 
 
“That led us down the road of who uses pure titanium,” Kaye says. “That could come from one or two places. Either the plant that manufactures it, or at that time they were using titanium in chemistry plants.” 
 
Using the electron microscope to further investigate the tie, Kaye and his team discovered a chip of aluminum and a piece of stainless steel. Those finds allowed the citizen sleuths to narrow their case. 
 
“There’s a second piece of evidence pointing toward a chemical plant,” Kaye says. 
 
Open Case
 
The team’s discoveries led them to think Cooper probably worked as a manager or engineer in a metalworking plant that processed titanium, or as an employee at a chemical plant. 
 
More importantly, the discoveries made the team doubt that anyone on the FBI’s current list of suspects is D.B. Cooper. 
 
“We don’t feel that any of the current crop of suspects have anything to do with the crime,” Kaye says. 
 
It’s difficult to know if the D.B. Cooper case will ever be solved. Many think Cooper could not have survived his parachute jump into the Pacific Northwest wilderness. If he did survive, the criminal is most likely in his eighties. 
 
Kaye thinks science and time will help close the case. 
 
“Maybe a hydrologist can use the latest technology to trace the $5,800 in ransom money found in 1980 to where Cooper landed upstream,” he says in an FBI article. “Or maybe someone just remembers that odd uncle.”
 
“We are hoping that when he dies,” Kaye says, “someone who knows something about him comes forward.”
Citizen Sleuths
D.B. is still at-large.
Microscopic Investment?
Most people don’t own electron microscopes. Many researchers get to use a university’s electron microscope for just an hour or two. Tom Kaye bought his electron microscope on eBay, and he said it has been a very worthwhile investment. 
 
“It’s been absolutely beyond words worth it,” he says. “You can’t imagine the world you can investigate with an electron microscope. You go to a place where no one has gone before.”
accumulate
Verb

to gather or collect.

alloy
Noun

mixture of two or more metals.

Noun

the distance above sea level.

chemistry
Noun

study of the atoms and molecules that make up different substances.

compile
Verb

to put together.

crowdsource
Verb

to collect and use work contributed by the public, usually through an internet-driven campaign, toward a specific project or goal.

debate
Verb

to argue or disagree in a formal setting.

dredge
Verb

to remove sand, silt, or other material from the bottom of a body of water.

electron
Noun

negatively charged subatomic particle.

electron microscope
Noun

powerful device that uses electrons, not light, to magnify an image.

engineer
Noun

person who plans the building of things, such as structures (construction engineer) or substances (chemical engineer).

evidence
Noun

data that can be measured, observed, examined, and analyzed to support a conclusion.

forensic investigator
Noun

person who works with law-enforcement agencies to solve crimes, often using science and technology.

forest
Noun

ecosystem filled with trees and underbrush.

hijack
Verb

to steal a transportation vessel, such as a truck or plane, or the cargo it is carrying.

hydrologist
Noun

person who studies the distribution, circulation, and properties of water.

manufacture
Verb

to make or produce a good, usually for sale.

metallurgist
Noun

person who studies the properties of metals and the technologies used in extracting them from ores, refining them for use, and creating alloys and useful objects from them. 

paleontologist
Noun

person who studies fossils and life from early geologic periods.

particle
Noun

small piece of material.

perpetrate
Verb

to commit or engage in.

pollen
Noun

powdery material produced by plants, each grain of which contains a male gamete capable of fertilizing a female ovule.

ransom
Noun

fee associated with the release or return of property.

sandbar
Noun

underwater or low-lying mound of sand formed by tides, waves, or currents.

silver chloride
adjective, noun

white, granular compound (AgCl) that darkens on exposure to light, often used in fingerprinting and photo-processing.

sleuth
Noun

detective or investigator.

stainless steel
Noun

metal that is very resistant to rust.

technology
Noun

the science of using tools and complex machines to make human life easier or more profitable.

titanium
Noun

chemical element with the symbol Ti.

upstream
Adjective

toward an elevated part of a flow of fluid, or place where the fluid passed earlier.

Noun

environment that has remained essentially undisturbed by human activity.