This mixed methods research study aimed to explain and understand user acceptance of an electronic performance support system (EPSS) designed for the Crime Scene Investigation and Identifi cation Units of the Turkish National Police. Quantitative data were collected from 209 police officers through a questionnaire to test relationships hypothesized in the technology acceptance model. At the same time, qualitative data were collected through interviews with 15 police officers to acquire an in-depth understanding of perceived usefulness and perceived ease of use of the system. This study showed that perceived usefulness, perceived ease of use, and attitude toward using were significant determinants of the acceptance of the EPSS. The findings also presented several user personal, system, and organizational characteristics that were considered as influencing factors for usefulness and ease of use of the EPSS.