It was one of the most shocking crimes in Colorado history — and the first case of a commercial airliner brought down by a bomb.

On November 1, 1955, United Air Lines Flight 629 — a Douglas DC-6B named Mainliner Denver — exploded in midair over Weld County, eight miles east of Longmont. The plane had just taken off from Denver, bound for Portland and Seattle.

All 44 people on board — 39 passengers and five crew members — were killed instantly. The ages of the victims ranged between 13 months & 81 years old. Investigators soon discovered that a dynamite bomb, using multiple sticks of dynamite, hidden in checked luggage caused the blast.

The luggage belonged to a passenger named Daisie King — and the bomber was her own son, 23-year-old John Gilbert Graham. Authorities said Graham planted the bomb to collect on his mother’s life insurance and out of resentment from his troubled childhood.

He was arrested within two weeks, after investigators traced the bomb materials and the insurance policy to him.

Graham was convicted of first-degree murder in 1956 and executed the following year — the first person in U.S. history to be put to death for bombing a commercial aircraft. It was the first ever trial to be televised in the State of Colorado.

The tragedy of Flight 629 led to major changes in airline security and baggage screening, reshaping how investigators handled sabotage in aviation for decades to come. On July 14, 1956, a bill was introduced, making intentional bombing of a commercial airline illegal. It was signed in to law by then President Dwight D. Eisenhower.