Although police organizations have devoted considerable effort to training investigators in evidence-based witness interviewing techniques, there is some suggestion that current practices do not meet the multifaceted requirements of sexual assault cases. Here, we assessed the specific challenges inherent in conducting interviews with adult sexual assault complainants, by conducting in-depth interviews with 21 experienced investigators from both Australia and New Zealand. The challenges that investigators identified fell into three broad themes: meeting the evidential needs of sexual assault investigations, establishing credibility, and managing complainant vulnerabilities. We discuss how the investigative interview process might be modified in line with these challenges.