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Critique of Citizen Sleuths Probability Calculation of DB Cooper’s Tie

The DB Cooper Case is notable for its lack of physical evidence. On the airplane, Cooper left behind some cigarette butts, two leftover parachutes, a glass he used and a black clip-on tie. The cigarettes were misplaced and are considered lost, there may or may not be DNA in evidence from them. Cooper’s fingerprints were likely collected from the airplane, as about 60 sets of fingerprints were recorded. The big piece of evidence was the tie. Recent testing done by Tom Kaye has uncovered evidence on the tie [found on Cooper’s seat] that gives the clearest profile yet of who Dan Cooper was before the heist. Since it can’t be known for sure if the tie was actually Coopers, Kay et al performed a probability analysis.

Here are the components of the CS team analysis: 1) Twenty passengers potentially leaving a tie on Cooper’s flight including Cooper. 2) Forgetting the tie on the plane = 15% (best estimate). 3) Leaving the tie on Coopers seat = 5% (best estimate). 4) Smoker = 44% (percentage of males who smoked in 1970). 5) Passengers wearing a black tie = 35% (best estimate). From these numbers, it is concluded there is a “98% probability” the tie belongs to Cooper.

There are a few areas where Kaye and his team might have gone wrong. Most glaringly is the fact, with the back door of the aircraft open and a man jumping off the airstairs while in flight, the cabin in the aircraft would have experienced significant pressure changes, making the odds a tie landed on Cooper’s seat after being blown from somewhere else, much higher. To give a more conservative estimate, variable #3 should be adjusted upwards, perhaps to as high as 25%. This adjustment gives us an approximate 90% probability the tie belongs to Cooper. Still high enough to affirm Kaye’s later analysis of the particles on the tie, but it does not cross the “two sigma threshold” Carr concludes. It’s a minor point, but an important one.

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