One thing to remember is that the hijacker was emphatically not called "D B Cooper". When he bought the ticket at the counter he called himself "Dan Cooper" but wasn't asked for ID as was normal then. When the FBI started investigating they found a known criminal in the area whose name was DB Cooper but he was interviewed and cleared.
In the rush to print, a reporter transposed the two names he had heard from the FBI and thus the perpetrator was christened DB Cooper and an urban myth was born...........