At about 4:30 p.m., September 14, 1924, Patrol Inspector James F. Mankin was killed by the accidental discharge of a Service rifle. The accident occurred about 18 miles northeast of Laredo near the Rio Grande River where Patrol Inspector Mankin, along with Patrol Inspectors Buck West and Ralph R. Dockum, were patrolling in a government vehicle. The officers, upon reaching the banks of the river, alighted from the car to determine whether or not any crossings had been made. Upon returning to the car, Patrol Inspector Mankin, who had been driving, entered the vehicle and seated himself behind the steering wheel. Patrol Inspector Dockum prepared to enter the back seat of the car from the left side and Patrol Inspector West was to enter the back seat from the right side of the automobile. There were two rifles in scabbards in the back of the car along with camping gear and other articles. The two officers were rearranging the items in the back of the car in order to make more room for themselves when a .30 caliber government rifle slipped out of the car, the hammer striking the running board and discharging the gun. The bullet struck the back of the front seat about six inches below the top. The bullet split, one part ricocheting to the left, striking the bow over the back seat and passing within a few inches of Dockum's face. The other part of the bullet ricocheted to the right through the upholstering of the front seat, striking Inspector Mankin behind the right ear. Inspector Mankin died less than thirty minutes after the accident.