Public and media scrutiny has raised concerns around police officers' abilities to prevent and deter sex offending, eroding public trust and compromising legitimacy beyond repair. Despite this, the relationship between self-legitimacy and the specialism for sex offences is under-explored. The study addressed this gap by drawing on constructivist interviews with 26 police officers. Participants emphasised the importance of investing in nationally recognised specialist practices to restore public trust and procedural fairness. For sex offences, specialism promoted legitimacy: internally by reinforcing officers’ confidence and role clarity; externally by improving credibility and victim engagement. Misalignments between public expectations and officers’ capacity were highlighted. Prioritising effective specialism could help constabularies rebuild public confidence for the investigation of sex offences and crime more broadly.