Since the analysis of complex services systems by using mathematical modeling techniques, with considering the random patterns prevailing in them, is so difficult or probably impossible, improvement guidelines are often followed based on the experts' experiences using qualitative methods. In the present paper, by employing a discrete event computer simulation methodology, criminal trial system has been quantitatively analyzed in a selected court in Iran and appropriate operational strategies to improve a couple of system performance indicators have been provided using sophisticated statistical tools such as design of experiments, hypothesis testing, regression analysis, sensitivity analysis and multi-objective optimization. Simulation results show possibility of a 27% reduction in average responding time on penal claims and simultaneously 80% reduction on repeated referral rate. Also, in order to examine analytical details, computer simulation model was validated using hypothesis testing method on a few dummy response variables.