This paper explores the relationship between urban public transportation innovation and crime. In 2004, the city of Medellin in Colombia developed an innovative public transportation system based on cable cars (Metrocable) to reach dense, isolated and dangerous neighborhoods. Using Spatial Difference in Difference approaches and a rich dataset at spatial analytical level, using max-p modeling, we explore the effects of the Metrocable on crime and its mechanisms. We find a significant impact on homicides reduction in the treated neighborhoods, especially in the medium run. Homicides decreased around 41% more than the general crime reduction in the city between 2004 and 2006, and by 49% between 2004 and 2012. We explore two mechanisms through which this intervention may affect the level of criminality, one is reducing the travel costs and improving accessibility to the rest of the city for low-income population (socioeconomic mechanism); the other is the increasing of the probability of apprehension for potential and active o enders (deterrent mechanism).