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## The Evidence Left Behind
What Cooper left on the plane was limited but real.
The black clip-on tie was recovered. It was sent to the FBI laboratory. Over the years, scientists have extracted various materials from it. A partial DNA profile was developed from the tie by approximately 2007, and for a period the FBI expressed some optimism that the profile might eventually help identify Cooper if a suspect could be compared. However, the profile was described as too incomplete to conclusively link to a specific individual, and the basic problem remained: a clip-on tie worn briefly by a man can carry the DNA of other people who handled, cleaned, manufactured, or came into contact with it. The tie’s wearer and the tie’s DNA are not automatically the same person.
More recently, FBI files released under public records requests have disclosed that analysis of the tie found more than 100,000 microscopic particles, including bismuth and unalloyed titanium. Researchers outside the FBI have speculated that this combination might suggest a connection to a specialized manufacturing environment—one researcher has pointed toward Boeing facilities, given the unique properties of some of the particles. The FBI has not endorsed a specific interpretation of this finding.
A hair found on the headrest of seat 18C was collected as evidence. It was not available for DNA testing; by 2002, the headrest hair had been lost from the FBI’s evidence inventory.
Eight cigarette butts were collected from the plane’s ashtrays—Cooper had smoked during the flight. The butts were sent to the Las Vegas field office for handling. Before any DNA testing could be done on them, they were destroyed. The precise circumstances of this loss have not been fully explained in public FBI communications.