and firearms. >> sean: two of the most ruthless and fastest growing transnational gangs are 18th street and ms-13. >> both are two of the largest tpwapbgss in the nation, originated out of this city. >> the gangs have taken control of this area. most of the people here are undocumented so they are scared to call the police, because they fear they may be deported. [ speaking spanish ] >> sean: ms in the 80s among immigrants fleeing a bloody civil war in el salvador. >> they were very used to violence. a lot of street violence was very natural for them. they were able to engage in that regularly. now ms-13 gang members engage in violence readily. they are not afraid to be violent against rivals even their own members who do not follow the rules. >> almost half of our 600 arrests over the last three