United Airlines Flight 629, registration N37559, was a Douglas DC-6B aircraft also known as "Mainliner Denver", which was blown up with a dynamite bomb placed in the checked luggage on November 1, 1955. The explosion occurred over Longmont, Colorado, United States at about 7:03 p.m. local time, while the airplane was en route from Denver, Colorado to Portland, Oregon and Seattle, Washington. All 39 passengers and 5 crew members on board were killed in the explosion and crash.Investigators determined that John "Jack" Gilbert Graham was responsible for bombing the airplane to kill his mother as revenge for his childhood and to obtain a large life insurance payout. Within fifteen months of the explosion, Graham—who already had an extensive criminal record—was tried, convicted, and executed for the crime.