Forensic psychiatric patients constitute a heterogeneous patient group, with common comorbidity within the externalizing spectrum. Increased knowledge on early antecedents in the pathway to severe mental illness and criminality is needed. In this study, we investigated early onset externalizing behaviors in three groups of forensic psychiatric patients 1) patients without contact with child and adolescent psychiatry (CAP), 2) patients with CAP contact, and 3) patients with both CAP contact and institutional placement. Participants (N = 98) were consecutively recruited from a cohort of forensic psychiatric patients in Sweden between 2016 and 2020. Data were collected through file information and semi-structured interviews and analyzed with a Bayesian approach. A history of CAP together with an institutional placement during childhood or adolescence was associated with more externalizing disorders, a higher number of convictions over the lifetime, a lower age at first conviction, and a lower age at first self-reported crime. Our findings provide further insight into the importance of early-onset adverse behaviors in the development of later externalizing behaviors, and may be of particular use for practitioners within social services and CAP services.
