From The Art and Popular Culture Encyclopedia
"Round up the usual suspects" is a line from the last scene of Casablanca, after Rick Blaine (Humphrey Bogart) has shot the German officer in charge of controlling Morocco's Vichy administration. It is spoken by Captain Renault (Claude Rains) to a group of Moroccan policemen, thereby hiding Rick's culpability in the killing of Major Strasser and the escape of Victor Lazlo, as well as showing Renault's anti-Nazi and pro-Allied sentiments. The phrase has since entered the lexicon of the English language.
This quote was ranked #32 on the American Film Institute's list of the 100 most memorable movie quotes in American film. It is also referenced in the title of the movie The Usual Suspects. Raul Julia used it in the movie Moon Over Parador.