United Air Lines Flight 629, registration N37559 and dubbed Mainliner Denver, was a Douglas DC-6B aircraft that was blown up on November 1, 1955, by a dynamite bomb placed in the checked luggage.

[1][3] Investigators determined that John Gilbert Graham was responsible for bombing the airplane in a bid to kill his mother as revenge for his childhood and to obtain a large life insurance payout.

[1] United Airlines Flight 629 had originated at New York City's La Guardia Airport on November 1, 1955, and made a scheduled stop in Chicago before continuing to Denver's Stapleton Airfield, landing eleven minutes late at 6:11 p.m.[1] At Denver the aircraft was refueled with 3,400 US gallons (2,800 imp gal; 13,000 L) of fuel and had a crew replacement.

[1] Captain Hall, a World War II veteran, assumed command of the flight for the segments to Portland and Seattle.

[1] Numerous telephone calls soon began coming in from farmers and other residents near Longmont, who reported loud explosions and fiery debris falling from the night sky—the remains of Flight 629.

[1] Extensive in-air breakup of the entire aircraft had occurred, and major portions of the wings, engines, and center sections were found in two craters 150 feet (46 m) apart.

Suspicions that a bomb had been placed in luggage loaded aboard the aircraft were fueled by the discovery of four pieces of an unusual grade of sheet metal, each covered in a gray soot.

Further testing of the cargo pit showed that each piece was contaminated with chemicals known to be byproducts of a dynamite explosion,[1] the origin of which was believed to be a passenger's luggage.

[4] One such insuree, as well as local, was Daisie Eldora King, 53, a Denver businesswoman who was en route to Alaska to visit her daughter.

When agents identified King's handbag, they found a number of newspaper clippings containing information about her son, John Gilbert Graham, who had been arrested on a forgery charge in Denver in 1951.

[4] Therefore, on the day after Graham's confession, the district attorney moved swiftly to prosecute him via the simplest possible route: premeditated murder committed against a single victim—his mother, Daisie Eldora King.

[9] He was convicted of the murder of his mother and, after a few short delays, was executed in the Colorado State Penitentiary gas chamber on January 11, 1957.

[11] The bombing of United Flight 629 is depicted in the opening segment of the 1959 film The FBI Story, starring James Stewart and Vera Miles.

[12] Graham was reportedly inspired to commit the crime by hearing of a similar incident, the Albert Guay affair in Quebec, in 1949.