On October 10, 1933, a Boeing 247 propliner operated by United Air Lines and registered as NC13304, crashed near Chesterton, Indiana. The transcontinental flight, carrying three crew and four passengers, had originated in Newark, New Jersey, with its final destination in Oakland, California. It had already landed in Cleveland and was headed to its next stop in Chicago, but exploded en route. All aboard died in the crash, which was proven to have been deliberately caused by an on-board explosive device ...

Melvin Purvis, head of the Chicago office of the United States Bureau of Investigation  described the damage: "Our investigation convinced me that the tragedy resulted from an explosion somewhere in the region of the baggage compartment in the rear of the plane ...

Despite the efforts of the investigators, no suspect has ever been identified or charged in this incident, and it remains unsolved.

This is thought to be the first proven act of air sabotage in the history of commercial aviation ...