Harmful sexual behavior (HSB) in individuals with autism spectrum disorder (ASD) and Intellectual Disability (ID) poses unique clinical and forensic challenges inadequately addressed by standard models. This study adapts the Integrated Theory of Sexual Offending (ITSO) via a biopsychosocial lens to analyze neurodevelopmental influences on HSB. Archival data from de-identified forensic archives (N=62 cases, ages 16-45, 2020-2025) from UK/US clinical facilities included ARMIDILO-S risk assessments (n=42), sensory profiles (n=38), and behavioral incident reports (n=55). Triangulation incorporated semi-structured interviews with 12 practitioners (45-min each). Ethical approval was obtained (IRB Ref: ETH-2025-012). Standardized variables comprised Theory of Mind (ToM) scores (M=45.2, SD=12.1), sensory sensitivities (M=3.8/5, SD=1.2), and isolation indices (M=4.1/5, SD=0.9). Aggregated descriptives and covariance matrices (Supplement A) informed preliminary Structural Equation Modeling (SEM) using Mplus 8.8. Preliminary SEM on this aggregated forensic cohort suggests Neuro-Ontogenic Vulnerability (ToM loading=0.88, sensory=0.74) as the primary HSB driver (β=0.85, 90% CI: 0.72-0.94), with secondary Contextual Deprivation (β=0.40, CI: 0.28-0.52; covariance=0.32). Model fit: CFI=0.96, RMSEA=0.045. Approximately 10-15% of forensic ASD/ID adults exhibited HSB, often functional (95% attribution: sensory regulation/intimacy-seeking) rather than predatory, linked to psychosexual education deficits and isolation. ITSO reframes cognitive distortions as ToM deficits, not denial. Findings advocate disability-informed risk assessment over punitive measures, emphasizing skill-based interventions. Robustness checks (bootstrapping 5,000 resamples; multi-group SEM) confirmed stability, though forensic bias limits generalizability.