The Silent Witness.

Janet Rigsby loves Richard Morgan, a Denver college student, but loses him when he is caught in a fire. Shortly after Richard's presumed demise, Janet leaves her home and bears a son out of wedlock. Over the years, she struggles to make ends meet while raising Bud, her son, on her own. Although her savings are small, Janet manages to send Bud to college. Chastised for his poverty and illegitimate birth, Bud, who is in love with the college gardener's daughter, suffers the ridicule of his peers and eventually comes to blows with and threatens one particular boy for insulting his mother. In the ensuing confrontation, the boy is killed and Bud is arrested for the crime. During the course of the trial, Bud discovers that the district attorney is Richard Morgan, his father. The testimony of one expert witness reveals how the murder in truth was committed, and a liberated Bud happily reunites with his mother and new-found father.