The Ox-Bow Incident (1942)

1885. When transient cowboys Gil Carter and Art Croft return to Bridger's Wells, Nevada to connect with Gil's girlfriend Rose Mapen, they learn both that Rose has left town without a word and that the rustling situation that had been occurring in the area when they were last through town has gotten worse. This trip through town coincides with news that the unknown rustlers have killed Larry Kincaid, a well known and well liked local rancher, his cattle gone. Most of the men of the town want to see quick justice, and without the Sheriff available, they form an unofficial posse. Regardless, the recently deputized Butch Mapes illegally deputizes all the people - which includes Ma Grier - who want to be part of the posse, they working on a majority rules basis. Thus, in reality, this group is a lynch mob, who will kill who they believe to have killed Kincaid. Gil and Art decide to join the group solely because, as relative outsiders, they are the most likely possible candidates as the rustlers, and thus want to steer the suspicion away from themselves. Also included in the group are Major Tetley and his generally coward son Gerald Tetley. The sadistic take-charge Major wants to impart on Gerald a sense of what he considers being a man, while the Major has failed to mention to Gerald that his credentials are all airs as he never saw battle during the war. The posse comes across three men in Ox-Bow Canyon who they believe to be the rustlers based on circumstantial evidence: Donald Martin, a rancher and family man who has just moved to the area, whose cattle he admits were Kincaid's but from who he swears he purchased them; Alva 'Dad' Hardwicke, Donald's aged slightly senile ranch hand; and a Mexican accompanying them named Juan Martínez. While the majority want to hang the three right then and there, there is a small group, including Gil and Gerald, who want this to be a true posse to allow the wheels of legal justice to determine the three's guilt or innocence, which means keeping the three alive until the Sheriff's arrival to take them into

IMDb: https://www.imdb.com/title/tt0036244