 The student movement has not been free from the influence of radical groups . This influence intensified in the 1960s , during the government of Carlos <unk> Restrepo , who initiated a repressive and military approach to the university conflicts . Since then , there have been confrontations between radical groups , from inside and outside of the university , and the police , in the campus grounds and its surroundings . On some occasions this resulted in participants being injured or even killed . On April 4 , 2001 , during a confrontation between masked individuals and the Mobile Anti @-@ Disturbance Squadron ( Spanish : <unk> <unk> <unk> , <unk> ) , police patrolmen John Arce was killed by an explosive . This incident was followed by the incursion of the police force into the university , which left equipment , buildings , and vehicles damaged . On September 22 , 2005 , during a protest against the Free Trade Agreement between the United States and Colombia , the chemistry student Jhonny Silva <unk> was killed , according by some witnesses , by the police force . 
