It was not possible to model causal mechanisms empirically in this case-control study, although our adjusted models suggest that raised suicide risk seen in people with a criminal justice history is partly explained by high prevalence of mental illness and, to a lesser extent, by the presence of social risk factors. Adjustment for psychiatric admission alone accounted for around half of the increased risk found. However, for many people, onset of psychiatric illness may lie on a causal pathway between criminal offending and suicide, and so this apparent confounding effect may be somewhat exaggerated. Alternatively, the adjusted estimates may be affected by residual confounding. From 1995, we also had access to all outpatient episodes as well as inpatient psychiatric care. We conducted a sensitivity analysis, restricted to 2000 to 2006, which showed that adjustment for any secondary care, as opposed to inpatient treatment only, did not materially alter the effect size estimates. Further adjustment for mental illness treated only in community settings may have attenuated the estimates further still. However, these data were unavailable and we know of no relevant population-based sources from elsewhere that could address this issue. We did not conduct separate analyses with adjustment for secondary care–treated drug/alcohol misuse because these conditions are known to be greatly underreported in the Psychiatric Central Register,54 and in any case, these diagnoses were included in our overall adjustments for all psychiatric admissions. Opiate dependency, in people with or without psychiatric treatment, may be a particularly important omission, because this group is prone to repeated property offending, criminal justice system contact, and custodial sentencing.55 A further potential confounder that was unavailable was low IQ, which has been shown to be linked with both criminal offending56 and suicide57 in population-based studies.