Characteristics of mentally retarded criminal offenders in Northern Taiwan.

The characteristics and criminal behavior in mentally retarded individuals remain largely unstudied. This retrospective study sought to establish a set of reference of criminal behavior characteristics in an ethnic Chinese mentally retarded group. Data were collected from forensic psychiatric evaluation of 32 mentally retarded offenders. Of the 32 offenders, only four (12.5%) cases were female. Mean age at the time of the offenses was 31. By IQ testing, 23 (71.9%) of the group fell into the mild mental retardation range, seven (21.9%) into the moderate mental retardation range, and two (6.2%) into the severe mental retardation range. Nineteen (59.3%) of the group also suffered from additional mental disorder. Eight (25%) had definite neurological deficit. Fourteen (43.8%) were repeat offenders. A total of 24 (75%) of the offenders had committed crimes against property, with 13 having committed petty theft. Furthermore, the pattern of offending shows differences from that of the general population or other mental disorders. The property offenses, especially petty theft and arson, were frequently seen. There was no noteworthy above average frequency of sexual offenses.