On Monday, a US Border Patrol agent on a bike shot and killed a 15-year-old Mexican boy for allegedly throwing rocks at him. When FBI agents arrived, Mexican authorities drew their weapons. Updated: Univision has video of the shooting.

The incident started when kids threw rocks at US Border Patrol agents who were riding bicycles on a bridge between El Paso, Texas, and Ciudad Juarez. Apparently rock throwing is a crime punishable by death on the spot, so one agent shot and killed 15-year-old Sergio Adrián Hernández Huereka. Mexican authorities say Hernández was shot inside Mexico. Border Patrol says he was trying to illegally cross into the US (and he was throwing rocks). Hernández's father told AFP, "There were lots of kids and the border patrol cop... started firing off shots and hit my son, my baby twice in the head."

As FBI agents arrived on the scene, Mexican police officers aimed rifles at them. FBI spokeswoman Andrea Simmons told The Dallas Morning News, "It pretty quickly got very intense over on the Mexican side." Obviously the Mexicans escalated this whole thing! Now US and Mexican officials are throwing accusations back and forth. From The Dallas Morning News:

Hernández was found 20 feet inside Mexico, and an autopsy revealed that the fatal shot was fired at a relatively close range, according to Arturo Sandoval, a spokesman for the Chihuahua state attorney general's office. Mexican authorities said a .40-caliber shell casing was found near the body, suggesting that the Border Patrol agent might have crossed into Mexico to shoot the boy. That would violate the rules for Border Patrol agents, who are supposed to stay on the U.S. side –- and could open the agent to a Mexican homicide prosecution.

Update: Via commenter Poop Cooper, we have exclusive video from Univision of the shooting. I don't speak Spanish so I can't provide context, but the actual shooting is pretty clear.

[Video via Univision; Image via Getty]