The title comes from a line in the classic film
Casablanca (1942), where the corrupt police chief, anxious to cover up the murder of a Nazi officer, tells a subordinate to "round up the usual suspects," meaning that the police should question a bunch of criminals who are known to be prolific. In the film, the criminals are rounded up without any evidence specifically pointing to them. The police are hoping to randomly get one of them to confess. Thus, they are the "usual suspects" because they have been convicted of crimes that relate to the one for which they have previously been arrested.
