Conversation so far:
what was the significance of the sleepy lagoon trial
The Sleepy Lagoon case was one of the major civil rights cases of the 1940s and exacerbated ethnic tensions which culminated in Los Angeles' Zoot Suit Riots of 1943.
who was charged in the Sleepy Lagoon trial
Seventeen Latino youths were indicted on the murder charges and placed on trial.
who was the murder victim in the Sleepy Lagoon trial
José Gallardo Díaz was discovered unconscious and dying on a road near a swimming hole (known as the Sleepy Lagoon).

Question: what was the cause of his death
Self-contained rewrite: what was the cause of Jose Gallardo Diaz's death