Well a highschool teacher deciphered one of the letters soon after it was published... so the time wasting excuse doesn't work. As far as resources are concerne

Well a highschool teacher deciphered one of the letters soon after it was published... so the time wasting excuse doesn't work. As far as resources are concerned: "July 12, 2016 Update: The FBI has redirected resources allocated to the D.B. Cooper case to focus on other investigative priorities." -- https://www.fbi.gov/history/famous-cases/db-cooper-hijacking https://www.fbi.gov/history/famous-cases/db-cooper-hijacking Here is a much more simple explanation: the FBI is notoriously bad at anything involving encryption or novel dynamics. That is why the Secret Service was so heavily involved in the big hacker crackdown decades ago, because the FBI was totally lost in the sauce. Bank robbery, payrolling informants, and CP they've got down pat.