A group of amateur scientists say they’ve stumbled upon a key piece of evidence in the mystery of DB Cooper, the man behind the world’s most infamous skyjacking. The scientists were selected by the Seattle FBI to look for clues in the 45-year-old case, and they’re now uncovering evidence that Cooper may have been a Boeing employee all along.

DB Cooper was the name applied to an unidentified man who hijacked a Boeing 727 in the air between Portland and Seattle back in 1971, extorted a $200,000 random and then jumped out of the plane, parachuting to an uncertain fate. An extensive manhunt and FBI investigation turned up nothing, and the case has gone unsolved to this day. Most experts believed from the beginning that Cooper couldn’t have survived the jump, but no body was ever found and no one could even figure out who the man was.

But new potential leads link Cooper to the Puget Sound aerospace industry in the early 1970s, and the Seattle FBI is very interested in finally figuring out who the man is. The researchers have analyzed particles that were removed from the clip-on tie Cooper left behind after hijacking the jet, using a powerful electron microscope to examine 100,000 particles on the JCPenny tie, identifying particles including Cerium, Strontium Sulfide, and pure titanium, according to a King5 report.

These are not just random elements — they’re used in narrow fields for specific things, including for Boeing’s Super Sonic Transport plane that was being developed under the direction of the government in the 1960s and 1970s, the report states.

It suggests that Cooper may have actually worked for Boeing as an engineer or manager at the plants. Now, scientists want help from the public. They want theories on what the materials may have been used for to help them build a profile of the mysterious DB Cooper.