Border Incident (1949), directed by Anthony Mann.
Dark, gritty and violent tale of Mexican and American police penetrating a gang who smuggle illegal farm workers across the border and sometimes murder them. (Some news stories have been running for a long time).
Ricardo Montalban (age 29) is lethally suave as the Mexican federal agent who goes undercover as a farm worker. I remember liking him as another policeman in Mystery Street (1950).
There is a famously horrific scene of murder by farm machinery. Civics class narration at the beginning and end.
We have a great lineup of villains in this film:
Howard Da Silva
Charles McGraw (starred in The Narrow Margin (1952) and was the gruff fisherman in the diner in The Birds (1963))
Arthur Hunnicutt (grew a beard and played backwoodsmen)
Jack Lambert
John Alton photography. Early André Previn score.