On April 16, 1960, Patrol Inspectors Archie L. Jennings, Robert M. Chaldu, and Gordon G. Hanks were assigned to duty from midnight to 8:00 a.m. at a traffic checkpoint known as San Mateo Flats, on Highway 101, about 18 miles north of Oceanside, California. The operation was concerned primarily with locating deportable aliens and alien smugglers who were enroute from the border to interior destinations. All vehicular traffic was stopped and inspected with a view to determining the citizenship status of the occupants.

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At about 6:40 a.m., an automobile went through the checkpoint without slowing down, whereupon Inspector Chaldu pursued the car in a patrol vehicle. At that time, Inspector Jennings was manning the traffic check at the stop sign where vehicles are halted. A car driven by Mr. Francis J. Defazio approached the stop sign, and his car was struck from behind by a speeding automobile operated by Mr. Gabriel Montoya. On impact, Mr. Defazio's car went out of control and struck Inspector Jennings, knocking him 50 feet away. Mr. Defazio's car was later found to have catapulted some 698 feet beyond the checkpoint. Inspector Jennings was pronounced dead upon arrival at the hospital. The cause of death was listed as basilar fractures of the skull. In addition, he suffered numerous contusions, fractures, and lacerations.