People with intellectual disability are overrepresented in police incarceration and have increased susceptibility to procedural injustice, a lack of awareness of legal rights, and do not have proper custodial decisions. Nonetheless, the systematic identification of ID at the point of contact with the police is unstable and unstructured. This research will assess the usefulness of a Risk-Need-Responsivity (RNR)- based screening system for identifying intellectual disability at an early stage within a police custody environment. A cross-sectional screening study was done at three urban police custody units with a sample of 312 detainees (mean age = 29.4 years; 18.6% female). Trained custody officers administered a short RN-informed screening instrument that included cognitive, adaptive, and communication measures and compared them to a standardised clinical measure as the reference standard. Sensitivity, specificity, and predictive values, as well as indicators of custody outcome, were used to assess screening performance. The screening conducted by RNR showed 54 people (17.3 %) who might have an intellectual disability. The tool had a sensitivity of 0.84 and a specificity of 0.89 compared with clinical assessment, with positive and negative predictive values of 0.76 and 0.93, respectively. The people detected at the initial screening had a higher likelihood of having the relevant procedural modifications (68.5% vs. 21.4%; p < 0.001) and a lower risk of extended detention lasting over 24 hours (12.9% vs. 27.6%). The results imply that applying the principles of RNR to ID screening during police custody is not only possible but also efficient, as it enhances timely identification and allows needs-sensitive at-risk protection. Implementing such frameworks could make the systems less vulnerable and more procedurally fair towards intellectually disabled detainees.