Through years of postmortem examinations and anthropometric studies of criminals, the insane, and normal individuals, Lombroso became convinced that the "born criminal" (reo nato, a term given by Ferri) could be anatomically identified by such items as a sloping forehead, ears of unusual size, asymmetry of the face, prognathism, excessive length of arms, asymmetry of the cranium, and other "physical stigmata." Specific criminals, such as thieves, rapists, and murderers, could be distinguished by specific characteristics, he believed. Lombroso also maintained that criminals had less sensibility to pain and touch; more acute sight; a lack of moral sense, including an absence of remorse; more vanity, impulsiveness, vindictiveness, and cruelty; and other manifestations, such as a special criminal argot and the excessive use of tattooing.
Besides the "born criminal, " Lombroso also described "criminaloids, " or occasional criminals, criminals by passion, moral imbeciles, and criminal epileptics. He recognized the diminished role of organic factors in many habitual offenders and referred to the delicate balance between predisposing factors (organic, genetic) and precipitating factors (environment, opportunity, poverty).
Lombroso's research methods were clinical and descriptive, with precise details of skull dimension and other measurements. He did not engage in rigorous statistical comparisons of criminals and noncriminals. Although he gave some recognition in his later years to