The Rookie Cop [1939] [DVD]

When his friend Tom Hadley is picked out of a lineup as one of the men who robbed furs from a warehouse, rookie cop Clem Maitland uses his police dog, Ace, to refute the eyewitness. Clem found a portion of ripped overalls at the scene, and Ace's keen sense of smell would have identified Hadley, he argued. But Police Commissioner Hugh Thomas, who doesn't believe in the usefulness of dogs in the police force, is not convinced, and Hadley is arrested.. ~ imdb