Crimes and sentences in individuals with intellectual disability in a forensic psychiatric context: a register-based study

Aims To study associations between intellectual disability (ID) and sexual and violent offending among individuals subject to pre-trial forensic psychiatric assessment. To investigate sentences following pre-trial forensic psychiatric assessment in offenders with and without ID. Methods A population-based observational study using data from pre-trial forensic psychiatric assessments in Sweden (1997–2013), the Swedish National Crime Register and several other Swedish national registers. The study population consisted of 7450 offenders (87% men, 13% women) who were subject to forensic psychiatric assessment in 1997–2013, of whom 481 (6.5%) were clinically assessed as having ID. Results ID offenders were more likely than non-ID offenders to have a sexual crime as an index crime [26.2 v. 11.5%, adjusted odds ratio (OR) 2.7, 95% confidence interval (CI) 2.02–3.58] as well as previous convictions regarding sexual offending (10.4 v. 5.6%, adj OR 2.3, 95% CI 1.70–3.12). These associations were restricted to male offenders; sexual offending was uncommon among women. Comorbid attention-deficit hyperactivity disorder reduced the association between ID and sexual offending (adj OR 2.7 v. 3.1, p = 0.017), while comorbid autism spectrum disorder had no significant influence on the association (adj OR 2.7 v. 3.0, p = 0.059). Violent crime was equally common among ID and non-ID offenders. Offenders with ID were more likely than non-ID offenders to be sentenced to forensic psychiatric care or community sanctions and measures (such as probation, conditional sentences or fines) than to prison; however, 15% of individuals who received an ID diagnosis during the forensic psychiatric assessment were sentenced to prison. Previous criminal convictions, concurrent antisocial personality disorders and substance use disorders were associated with a higher probability of a prison sentence among offenders with ID. Conclusions Sexual crime is overrepresented among offenders with ID compared to offenders with other mental disorders than ID in forensic psychiatric contexts. ID offenders become subject to forensic psychiatric care and forensic psychiatric services need evidence-based treatment programmes for offenders with ID. In addition, there is a need for early intervention strategies suitable for disability services and special education schools, in order to address the complex needs of individuals with ID and prevent sexual and violent offending.