The People Against O'Hara is a 1951 film noir directed by John Sturges and based on Eleazar Lipsky's novel. The movie features Spencer Tracy, Pat O'Brien, and James Arness. Wikipedia
Det. Vincent Ricks: (Ricks brings in Frank Korvac) Here he is... people's witness. District Attorney Louis Barra: (Contemptuously) People's witness? People's slob!