This case study outlines the pathway to conducting a longitudinal, within-subjects intervention study with police officers. The focus of the intervention was to reduce lethal force errors by teaching police officers to modulate their stress response physiology. Using an established clinical intervention known to modulate stress physiology (heart rate variability biofeedback), the study was successful in reducing lethal force errors among police and improving health outcomes. We describe the importance of ecological validity, using multiple objective measures of outcomes, and practical issues in conducting longitudinal field research (e.g., staffing and resources). We outline the challenges of conducting empirical research in an organization and occupation that is unfamiliar with research and make recommendations for researchers interested in conducting future studies using similar methods within this population.