Sources : FBI : The violence sparks ` ` serious doubts about the use of lethal force '' Notimex : A U.S. Border Patrol agent shoots and kills an adolescent . Border patrol : An agent opens fire in response to rock - throwing . The FBI is investigating .
NEW : Mexico : The violence sparks `` serious doubts about the use of lethal force '' Notimex : A U.S. Border Patrol agent shoots and kills an adolescent . Border patrol : An agent opened fire in response to rock-throwing . The FBI is investigating .