NADD Bulletin Volume VI Number 4 Article 2

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The Identification of Clinically Relevant Subtypes of Criminal Offenders with Developmental Disabilities

Edwin J. Mikkelsen, M.D.

The assessment of risk in individuals with developmental disabilities who commit criminal offenses is predicted on a number of different factors. These factors include the individual's prior offense history with regard to frequency, severity, and typology. The likelihood of future offenses is also affected by personal characteristics that have been referred to as "destabilizing factors." Primary destabilizing factors that are referred to in the literature are untreated major mental illness and/or active substance abuse (Mikkelsen & Stelk, 1999).

Within this broad framework, it may be possible to make further meaningful clinical distinctions based on the pattern of offenses, if it is consistent over several years.

There are few long-term follow-up studies of offenders with developmental disabilities, and the numbers involved are usually small. Day (1988) has provided a detailed report concerning 26 patients who were admitted to a specialized hospital-based treatment program for offenders with developmental disabilities during the years 1974-1982. The I.Q.'s ranged from 58-81 (average 64.6) with 12 functioning in the mild range of developmental disabilities, and eight functioning in the borderline range. In 15 cases the discharge was planned, whereas the others left on legal grounds, escaped, or by other unplanned means. Only five went to supervised settings, while the others went to live with their families, or more independent settings. The follow-up period ranged from six months to five years, with an average of 3.3 years (eight individuals for five years and 16 for at least two years). Eleven individuals re-offended during the follow-up period, and six did so within the first year. Eight individuals re-offended between two to four times. The risk for re-offence was greatest in the immediate post-discharge period. The author noted that there was a significant difference in outcome when one looked at the type of offense. Specifically, the investigator made a distinction between "Offenders Against the Person" and "Property Offenders." When this comparison was made, "only 42% of the Offenders Against the Person (assaulters and sex offenders) had subsequent convictions, as against 88% of the Property Offenders (arsonists and property offenders)." The difference was found to be statistically significant at the 0.05 level. There were no significant differences between the groups with regard to the duration of inpatient treatment, length of follow-up, or quality of outpatient care. However, it was noted that "seven of the twelve Offenders Against the Person received regular tranquilizing or sex-suppressant medication throughout the follow-up period, as compared with only one of the eight Property Offenders (p<.0.5)." A subsequent record review of 47 male sexual offenders with developmental disabilities from the same treatment center provides additional information with regard to the subtypes of offenders with developmental disabilities (Day, 1994).

The I.Q. distribution of this study group was borderline I.Q. (23%), mild (58%), and moderate (19%), with a mean I.Q. of 59.5. The average age was 23.9 years.

The authors reported several findings including, "Statistical analysis identified two distinct groups of mentally handicapped sex offenders, the principal differentiating characteristic being whether or not they had also committed non-sexual offenses." The results further indicate that for the "Sex Offenders Only group...the recidivism rate is high." However, "They tend to commit minor offenses and are rarely convicted." In comparison, those who have also committed non-sexual offenses were found to "...exhibit a high sociopathy, prevalence of psychosocial deprivation and brain damage, and tend to have lengthy histories of antisocial behavior...they are more likely to commit serious sex offenses and become persistent sex offenders."

Parallel, but independent, research concerning juvenile sex offenders has provided similar results. In a comprehensive study of 114 adolescent juvenile offenders (age-range 12-16 years, mean = 14.8; S.D. = 1.2), Butler & Seto (2002) identified four clinically relevant subtypes of offenders. Specifically, there were 34 "Non-aggressive Offenders;" 48 "Criminally Versatile Offenders (aggressive and non-aggressive crimes);" 32 "sex offenders" that were further subdivided into "Sex Only Offenders" (N=22) and "Sex Plus Offenders" (N=10). The authors then compared the "Sex Only Offenders" with the "Sex Plus Offenders" on a number of variables. The results indicated that "Sex Only Offenders had significantly fewer current behavior problems, more pro-social attitudes and beliefs, and a lower expected risk for future delinquency than did the Sex Plus Offenders." Further, the authors noted, "Sex Only Offenders victimized significantly fewer unrelated victims than did the Sex Plus Offenders" and "in many respects, the Sex Plus Offenders were similar to the Versatile Offenders."

The Sex Only offenders also, "...had significantly fewer current behavior problems, more pro-social attitudes and beliefs, and a lower expected risk for future delinquency than did the Sex Plus Offenders."

The purpose of the preliminary retrospective review of case material described in this manuscript is to determine: 1) If individuals were consistent in their offender profile over time; 2) The relative presence of the primary destabilizing factors of major mental illness and substance abuse within the different profile groups; and 3) Victim profile as it related to adults vs. minors and the offender's relationship to the victim.

There were too few cases of non-violent offenders to merit systematic review. This most likely represents societal response to this type of offense, which does not present a physical risk to others, and is not a reflection of the relative frequency of this behavior.

The history of two individuals that were identified as fitting this profile (one male and one female) indicated that compulsive repetitive stealing does exist, but is not apt to result in charges, although it may lead to the cessation of a community program.

There were several representative profiles of adults with more significant offense histories and for whom there was at least 10-20 years of history. The review of these profiles indicated that individuals could be grouped according to the categories of Physical Offenses Only, Sexual Offenses Only, and Sexual Plus Physical Offenses (Sex Plus). Ten representative profiles were selected from each category for review, with regard to the factors cited above.

1.Physical Offense Only (N=10): Within this category there were seven males and three females. Two of the females were diagnosed with a Borderline Personality Disorder, and one with a Mixed Personality Disorder. Of the seven males, two had a primary diagnosis of Psychotic Disorder, and the remaining five could best be described as having a profile consistent with Antisocial Personality Disorder and/or an Impulse Control Disorder. The offense pattern was as follows: Severe Physical Assault Only (N=5); Physical Assault in Addition to Pulling Fire Alarms (N=2); Arson (N=2); and Homicide (N=1). With regard to the relationship to the victims, four had attacked staff; one staff and peers; one peers only, one family members; and one staff and community members. The two individuals with arson both destroyed buildings in the possession of a member of the general community.

2.Sex Only Group (N=10): Within this group there were five individuals with a diagnosis of Major Mental Illness, which played a significant role in the offense history (Psychosis = 4; Bipolar Disorder = 1); while in two others alcoholism was a significant factor in the offense history. The others had a primary diagnosis of Pedophilia. The severity of sexual offenses ranged from exhibitionism and inappropriate touching, to rape of a child (N=3). All but one of this group had committed offenses against members of the broader community and only one against a family member. All of the offenses involved children.

3.Sex Plus Offenders (N=10): With regard to destabilizing factors, four of these individuals had a major mental illness in the form of a concomitant psychotic disorder. The severity of sexual offenses ranged from inappropriate touching to rape (N=5). The degree of physical assaults was severe, including two homicides. For the most part, the offenses were committed against caretakers and peers. One of the homicide/rapes involved a stranger, while the other homicide was of a female staff member. One individual committed a sexual offense (rape) against community members, but physical assault was usually directed to caretakers.

Summary and Conclusions

This preliminary review of case material is, in general, consistent with the earlier work of Day and the parallel study of Butler & Seto concerning adolescent offenders, in that the offenders who have displayed a consistent pattern of sexual aggression toward others, in addition to other types of aggression (the Sex Plus group), have presented with a more diffuse pattern of antisocial behavior and are more apt to assault caretakers. In this respect, they are more similar to the Physical Only offenders than to the Sex Only offenders However, the results with regard to the Sex Only offenders differ from Day's findings, in that within the group described here, the offenses were primarily directed toward members of the broader community who did not have a personal relationship with the offender, and the offenses were relatively more severe than those committed by the cohort described in the Day study.

The number of individuals discussed in the Day study and in this preliminary review of case material is relatively small and, thus, it would be premature to draw any definite conclusions about the relative risk presented by individuals whose pattern of offending is consistent with these profiles.


Butler, S. M. & Seto, M. C. (2002). Distinguishing two types of adolescent sex offenders. Journal of the American Academy of Child and Adolescent Psychiatry, 41, 83-90.

Day, K. (1988). A hospital-based treatment programme for male mentally handicapped offenders. British Journal of Psychiatry, 153, 635-644.

Day, K. (1994). Male mentally handicapped sex offenders. British Journal of Psychiatry, 165, 630-639.

Mikkelsen, E. J. & Stelk, W. J. (1999). Criminal offenders with mental retardation: Risk Assessment and the continuum of community-based treatment programs. Kingston, NY: NADD Press.

For further information:

Edwin Mikkelsen, M.D.

National Mentor Network

67 Yarmouth Road

Wellesley Hills, MA 02481