Although the falling crime rates in the 1990s surprised criminologists, it was not the first time crime had declined. There was a ‘crime drop’ in England in the 1920s. When crime did not rise as expected following the Great War, the government closed half the prisons, and Edwin Sutherland came to investigate ‘England’s empty prisons’. To conduct his analysis, Sutherland relied on work by SK Ruck, and between them, they came up with most of the leading explanations now used by criminologists. They considered the police and prisons, the economy and household security. They also discussed the psychological conditions of low-crime societies, the ‘sense of security’. Drawing on their unpublished material from archives in New York and London, the discussion here examines what can be learned about contemporary analyses of the crime drop of the 1990s. Overall, this article argues for the importance of theory in analysing the statistics of falling crime and how historical studies of crime trends can be useful in developing this theory.