Oscar was a gunman working for Busby Giles.
In 1936, Oscar was working in the Hopi cave when Indiana Jones was discovered and captured for a second time. While Busby Giles revealed his strategy to the professor, Oscar covered the cavern from a higher level. As Jones revealed that he had radioed the state patrol and sirens sounded in the distance, Giles and his daughter Lucy Giles made their escape, while Jones began fighting his thugs. One of the toughs called for Oscar to open fire with his machine gun. Oscar obliged, firing at Jones as he rolled near some crates and drums. Jones kicked over a fuel drum, which caught on fire from one of Oscar's ricochets. With a fire between him and the gunmen, Jones managed to escape.
It is likely that Oscar was eventually apprehended and rounded up by the state troopers when they came to arrest the criminal gang.