Denver, CO, November 1, 1955. United Airlines Flight 629, a DC-6B bound for Portland and Seattle, exploded in flames only 11 minutes after taking off from Denver. The subsequent crash in a farm field near Longmont, Colorado, killed everyone on board. It wasn't very long into the crash investigation when chemical residue, consistent with the explosion of dynamite, was found on debris from the rear baggage compartment. The crash investigation then turned into a criminal probe of the second act of sabotage of a commercial airline, in United States history.