CIUDAD JUAREZ, Mexico – Mexicans are seething over the second death of a countryman at the hands of U.S. Border Patrol agents in two weeks, an incident near downtown El Paso that is threatening to escalate tensions over migrant issues. U.S. authorities said Tuesday a Border Patrol agent was defending himself and colleagues when he fatally shot the 15-year-old as officers came under a barrage of big stones while trying to detain illegal immigrants on the U.S. side of the Rio Grande.