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70s aircraft hijacker D.B. Cooper believed to be a chemist
In November 2011, Kaye announced that particles of pure (unalloyed) titanium had also been found on the tie. He explained that titanium, which was much rarer in the 1970s than in the 2010s, was at that time found only in metal fabrication or production facilities, or at chemical companies using it (combined with aluminum) to store extremely corrosive substances.[93] The findings suggested that Cooper may have been a chemist or a metallurgist, or possibly an engineer or manager (the only employees who wore ties in such facilities at that time) in a metal or chemical manufacturing plant,[94] or at a company that recovered scrap metal from those types of factories.[95]In January 2017, Kaye reported that rare earth minerals such as cerium and strontium sulfide had also been identified among particles from the tie. One of the rare applications for such elements in the 1970s was Boeing’s supersonic transport development project, suggesting the possibility that Cooper was a Boeing employee.[96][97] Other possible sources of the material included plants that manufactured cathode ray tubes, such as the Portland firms Teledyne and Tektronix.[98]
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