East Side Kids (1940)

“Young street kid grows up and becomes a cop when he realizes that crime doesn’t pay. One of his childhood friends is in prison for a murder he didn’t commit, and the cop looks for evidence to free him. Meanwhile, the prisoner’s brother gets mixed up with a gang of counterfeiters, and inadvertently discovers the evidence that can set his brother free, if he can only get someone to believe him.” -imdb.com