Detective Ybarra (Kelly) travels to a ranch in Wineville, Riverside County, to arrange the deportation of 15-year-old Sanford Clark (Eddie Alderson) to Canada. The boy's uncle, Gordon Northcott (Harner), has fled after a chance encounter with Ybarra, who mentions his business there being a juvenile matter. Clark tells Ybarra that Northcott forced him to help kidnap and murder around twenty children, and identifies Walter as one of them. Jones tells Briegleb that Christine is in protective custody following a mental breakdown. Jones orders Clark's deportation, but Ybarra makes Clark reveal the murder site. Briegleb secures Christine's release by showing Steele a newspaper story about the Wineville killings that names Walter as a possible victim. Under interrogation by Ybarra, Walter's impostor reveals his motive was to secure transport to Los Angeles to see his favorite actor, Tom Mix, and says the police told him to lie about being Christine's son. The police capture Northcott in Vancouver, Canada. Christine's attorney (Pierson) secures a court order for the release of the other unjustly imprisoned women.
On the day of the city council's hearing into the case, Christine and Briegleb arrive at Los Angeles City Hall, where they encounter thousands of protesters who are demanding answers from the city. The hearing is intercut with scenes from Northcott's trial. The council concludes that Jones and Davis should be removed from duty, and that extrajudicial internments by police must be reviewed. Northcott's jury finds him guilty of murder and the judge sentences him to death by hanging.
Two years later, Christine has not given up her search for Walter. Northcott sends her a message saying he is willing to admit to killing Walter on condition that Christine meets him before his execution. She visits Northcott, but he refuses to tell her if he killed her son. Northcott is executed the next day.
In 1935, David Clay—one of the boys assumed to have been killed—is found alive in Hesperia, California. He reveals that one of the boys with whom he was imprisoned was Walter. David, Walter, and another boy escaped, but were separated. David does not know whether Walter was recaptured, giving Christine hope he is alive.
In the epilogue, it states that after the hearing, Captain Jones was suspended, Chief Davis was demoted, and Los Angeles Mayor George Cryer chose not to run for reelection. Rev. Briegleb continued to use his radio show to expose police misconduct and political corruption. Wineville changed its name to Mira Loma. Christine Collins never stopped searching for her son.