In Mexico, increasing demands for public safety coupled with the need for a more effective criminal justice system resulted in the security and justice constitutional reform of 2008. The outcome was a constitutional framework with provisions based on the highest standards of human rights on the one hand, and on the other, exceptional measures that restrict rights in an attempt to improve public safety. Unfortunately, the crime rate and incidence of unreported crime have changed little. When public safety is demanded, a clear, rational and concrete response is required. Limiting the alternatives to pre-trial detention or increasing penalties is rarely the appropriate response. This paper focuses on pre-trial detention and non-custodial measures supported by the new criminal justice system, how they relate to the principle of the presumption of innocence and the tension between this and the punitive demands for increased imprisonment. In addition, this study discusses a technical solution, found in pre-trial services, which seeks to balance the presumption of innocence and the right to personal liberty with public safety.