Background: Individuals with intellectual disability (ID) and autism spectrum disorder (ASD) are at increased risk of sexual abuse. However, little is known about facilitating detection and disclosure. One year after discharge from a specialised psychiatric ward, a young man with mild ID and ASD disclosed previously unknown sexual abuse. The aim of the present study was to explore clinicians' perceptions of their failure to detect abuse. Method: Interpretative phenomenological analysis was used to explore five staff members' perceptions, with data being collected through an individual, semi-structured interview. Results: Staff reported behaviours that, in retrospect, they understood as possible indicators of abuse and/or attempts by the patient to disclose. Factors contributing to non-detection included insufficient trauma sensitivity, lack of exploration, and diagnostic overshadowing. Conclusions: Symptoms of trauma should be routinely explored in individuals with ASD and ID referred for psychiatric assessment -- even in the absence of known trauma or abuse.