At 8:30 a.m., on Saturday, December 1, 1973, Missouri Pacific Railroad Company freight train Extra 615 South (train DMX) entered Cotulla, Texas. Train DMX was traveling on a nonsignalized main track at a speed of 35 to 40 mph. Just after it passed over a grade crossing, the train was diverted through a switch onto an adjacent track where an unmanned locomotive, a caboose, and 11 cars were standing. Train DMX collided with the standing locomotive before any appreciable braking. The collision derailed all of the locomotive units and 29 railroad cars. Three crew members who were riding in the lead locomotive unit of train DMX were killed.