Despite mentally disordered suspects being over-represented within the criminal justice system, there is a dearth of published literature that examines police officers' perceptions when interviewing this vulnerable group. This is concerning given that police officers are increasingly the first point of contact with these individuals. Using a Grounded Theory approach, this study examined 35 police officers' perceptions and experiences when interviewing mentally disordered suspects. Current safeguards, such as Appropriate Adults, and their experiences of any training they received were also explored. A specially designed questionnaire was developed and distributed across six police forces in England and Wales. Nine conceptual categories emerged from the data that highlighted how police officers' level of experience impacted upon their perceptions when dealing with this cohort. As a consequence, a new model grounded within Schema Theory has emerged termed Police Experience Transitional Model. Implications include the treatment and outcome of mentally disordered suspects being heavily dependent on whom they encounter within the criminal justice system.