( CNN ) -- At one time , teens Carlos Gonzalez , 16 , and Juan Carlos Echeverri , 15 , were classmates at Cathedral High School in El Paso , Texas . Like many who live along the border , both boys had strong ties to El Paso , and especially to neighboring Ciudad Juarez , Mexico . That 's where they found themselves on Saturday , where they were gunned down at a car dealership by unknown assailants . Gonzalez and Echeverri were both U.S. citizens , the Cathedral principal told CNN . A third youth , 16-year-old Cesar Miramontes of Juarez was also killed in the incident . `` Like many kids involved in this border reality of straddling two cultures , he had a lot of stress about what 's going on in Juarez , '' the high school principal , Brother Nick Gonzalez , said of Gonzalez . The two are not related . The young Gonzalez , the principal said , was `` mischievous , but a good kid . '' His family , which had lived in Juarez , had recently started renting an apartment in El Paso for safety reasons . Juarez is a flashpoint in the drug cartel turf wars that have left thousands dead over the past four years . There were more than 3,000 killings recorded in Juarez alone in 2010 . Moving to the United States , for any child , is a cultural shift , and `` I think he struggled with that , '' the principal said . Echeverri went to school with Gonzalez at Cathedral their freshman year , before he returned to Juarez to attend school there , the principal said . The shooting happened at 4:22 p.m. Saturday at a car dealership , where the teens were looking at cars , said Arturo Sandoval , spokesman for the Chihuahua state attorney general 's office . Police recovered at least 18 bullet casings at the scene from an AK-47 , an automatic weapon commonly used by drug traffickers in the city . `` We believe ( Echeverri ) and the two others had been friends for a long time . He was here in the city to visit them , '' Sandoval said . Virginia Staab , a spokeswoman for the U.S. State Department , said Monday that U.S. authorities are actively looking into the incident and had not yet confirmed the citizenship of any of the victims . Even though the killings happened in Juarez , they re-open wounds for the students and the community of El Paso , Nick Gonzalez , the principal , said . Seemingly everyone knows someone who has been killed , extorted , kidnapped or robbed , he said . Just because the violence is on the Mexican side of the border , does n't make it a Mexican problem , he said . `` It is not a 'them ' problem , it is an 'us ' problem . We need to find out how to help kids cope , '' he said . `` Just because there is a border does n't mean that the emotions and pain do n't cross over . '' Monday 's killings marked the first time that a current student at Cathedral High School was killed in the Juarez violence . But alumni have been killed before , and , just before Christmas , the father of a student -- a successful orthopedic surgeon in Juarez -- was kidnapped and killed . The fatal shootings come on the heels of numerous similar violent incidents in recent months in Juarez . In one 48-hour span last week , for instance , at least 14 people were killed -- including a municipal police officer and a newspaper vendor who police believe was targeted due to her job , according to Juarez Police spokesman Adrian Sanchez .
Three teens killed Saturday at a car dealership in Ciudad Juarez . Two of the victims were U.S. citizens , a school principal says . Ciudad Juarez has been beset by severe violence in recent months .