Jiro,
unfortuantely this incident comes down where the Border Patrol agent had to use deadly force is where he, or someone else is in immediate danger. I have read this thread and got amused with some of the comments. they don't realize how dangerous the rocks are. they are fist sized... not a pebbles and believe me they are constantly attacked when they apprehend those people who are entering the US illegally.
In this case that everyone is debating, this certain agent on mountain bike approached 5 to 6 males attempting to break the fence, however they ran back to Juarez and the agent attempt to restrain two individuals however got one. the group is trying to help the detained individual by throwing to the agent so the detained invidiuals can escape. The agent already gave a warning to the group to cease throwing rocks, they SIMPLY ingore his warning and kept throwing. He is now within his authority to protect himself and the detain individual by using deadly force. In worse scenairo if a rock hit the agent and injured him and possible dropping his firearm... the detained will attempt to use his firearm against the agent and kill him.
I have been there, and have seen the first hand of how those illegals are trying to muscle themselves into US and its not a pretty sight. Juarez is now having the highest murder rate in the North America, as of today over 1,100 have been killed even infants, toddlers, and young children were killed in the amushes by the drug cartels in broad daylights... extremely brutal if you ask. There were exdous of people and business coming into El Paso to stay away from this violence. in 2008 1,400 was killed, 2009 over 1,600 killed and right now we are alread exceeding in numbers from last year. I loved visiting Ciudad Juarez in the past, but I'm not taking any chance across there at this moment.
I fully support the BP agent what he did, someone use a weapon therefore he defends himself with a weapon. What other options what you will do if you are being thrown with rocks and nowhere to protect yourself.