Could you please provide a link that corroborates the above description? It doesn't seem to go along with what happened. The
video I've seen shows at least 4 individuals involved across a ten meter dried Rio Grande. (Maybe you just misremebered the facts rather than spinning the situation to better fit your impression. It wouldn't be very Christian of you to be disingenuous with the facts and then complain about others lack of compassion. People in glass houses shouldn't throw stones.....especially at border guards.
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FWIW the current Texas Middle School Boy's Shot Put (4kg) record is 50' 9" while the Girl's record (6lb) is 36' 10". While not the norm, clearly children this age are more than capable of throwing rocks the distance involved. I'd agree it's implausible for a 14y/o to throw a hand sized rock 100 yds but I have no doubt that the youths involved were capable of throwing stones large enough to cause harm the 10 meter distance.