One of the biggest challenges that the field of anti-human trafficking is facing is the lack of effective methods for victim identification. There are tools like hotlines, police investigations based on reports and training to relevant stakeholders but these fall short and many victims of trafficking are never found. To complement these actions it is necessary to implement surveillance systems among vulnerable populations such as migrants, agriculture and factory workers, fishermen, sex workers, internally displaced people and many other groups who are likely to experience or have experienced severe forms of exploitation. We propose the sentinel surveillance, a methodology borrowed from health sciences in order to track the prevalence, patterns and vulnerability factors among populations likely to encounter trafficking. This methodology has been applied before in the context of human trafficking by the UN at the Thai-Cambodian border to measure the prevalence of trafficking victims among Cambodians being deported from Thailand. This paper will explore the possibility of applying the methodology among demobilized combatants from illegal armed groups in Colombia with the hope of finding a relationship between recruitment into criminal gangs and human trafficking.