He published many books and essays on social and political problems, and exposed the unscientific theories of Cesare Lombroso and his Scuola positiva (Positive school)See for instance: Homicide and the Italians, by Napoleone Colajanni, The New York Times, March 24, 1901 and Enrico Ferri on criminology. Colajanni was particularly critical of Lombroso's biological determinism – in particular the alleged inferiority of southern Italians – and he put a much greater emphasis on social conditions as a cause of offending. Lombroso and his disciples, however, remained dominant in Italy.Emsley, Crime, police, and penal policy, p. 191
