The DNA profile developed from the tie in the mid-2000s was the most promising of these attempts, and it fell short. The partial profile was too incomplete. The basic problem of attribution—who left the DNA on the tie, and was it the wearer or someone else?—was not solvable with the material available.
The particle analysis has pointed in interesting directions without pointing at a specific person.
The tie is in the FBI’s evidence archive. It has not been returned to anyone. It remains, physically, the best preserved direct artifact from Cooper himself that exists in confirmed custody. What it can tell us about him appears to have limits that the methods available so far have not overcome.
—
## The Airstair and How It Changed
The Boeing 727’s aft airstair—the specific feature that made the Cooper hijacking possible—was a practical engineering solution to a practical problem. Short-haul flights often used airports without jetways, and the ability to deploy stairs from the aircraft itself allowed passengers to board and exit without external ground equipment.
The aft airstair on the 727-100 could be deployed from a switch inside the aircraft, and in early models it could be operated while the plane was airborne. This was not a widely discussed feature. It was an engineering characteristic of the aircraft, not something that appeared in passenger briefings or promotional materials.
Cooper knew about it. This knowledge—specific, operational, and not commonly held—has been one of the enduring arguments for the theory that Cooper had an aviation background or connection. The list of people in 1971 who would have known that the 727’s aft stair could be deployed in flight, and understood how to use that fact in a hijacking plan, was not a long list.