Feeblemindedness must be considered an abnormal personality characteristic that is conducive to criminal behavior. Factors associated with feeble-mindedness are poor nourishment in infancy, heredity, negative environmental influences, and the cultural and economic level of parents. Young persons with underdeveloped intelligence can be recognized by their poor school performance, thier narrow view of life and society and their inability to discriminate details and to reach logical conclusions. The interrogator must attempt to assess the extent of the interrogated individual's mental limitations by looking for such signs as a lack of concentration, temporal disorientation, speech problems, and delusions. At the same time, the forensic scientist must be on his guard because offenders frequently try to simulate psychoses or feeblemindedness. Statements by feeble-minded individuals must be corroborated with other evidence. Interrogating officers must also ascertain whether they are dealing with low intelligence or with mental deficiencies. Officers must keep in mind that individuals who are unable to manage their own affairs are under the protection of the state, and that their rights must be carefully protected. Leading questions can only be used with great caution. A general discussion with the individual can help to establish his or her level of understanding. Simple yes-or-no questions should be avoided because of the danger of misinterpretation or of unfair suggestion. Lying by feeble-minded individuals may be a direct consequence of their deficiencies. Sometimes the interrogator cannot obtain any useful information from the mentally deficient individual, except perhaps with the assistance of a specially trained expert. The interrogator must never forget that the statements and memories of mentally deficient individuals are easily influenced by complex courses of events and the opinions of others. Notes are supplied.