Bob Owens over at Pajamas Media has done a good job walking through the utter disaster that was Operation Fast & Furious (short version: the US government deliberately let Mexican narco-terrorist groups get their hands on illegally-purchased firearms). But note this paragraph:
The eventual — perhaps inevitable — death of a U.S. Border Patrol Agent killed by criminals armed with at least two “walked” AK-pattern semi-automatic rifles finally shut the program down in December of 2010. The shooting death of an American cop was the final straw for the ATF whistleblower who exposed the program, which may also have contributed to an estimated 150 or more Mexican police and soldier shootings, and many of civilians. Had a whistleblower come forward earlier, all might have been alive today.
Bolding mine. The 150 number also shows up here.
We've all been focused on the American killed by this, but it must be noted: if Brian Terry had not been shot we would still be in a position where we helped destabilize the domestic situation of a country that we're supposed to be friendly towards. You see, the US government apparently neglected to mention to the Mexican government that we were letting guns that we knew were going to be illegally resold continue to go over the border; if we had, the Mexican government might have asked some pointed questions about how this could be reconciled with existing agreements to... keep firearms from being illegally resold in Mexico. And even more pointed questions about why conducting what has been categorized as being a stealth political attack on Second Amendment rights is apparently important enough to justify letting Mexican nationals get murdered*.
Actually, I know the answer to that last one! It involves the phrase "Ugly American."
Moe Lane (crosspost)
*At some point you're going to hear somebody mutter "If it weren't these guns, they would have just used others" as a defense to this one. Feel free to first respond by saying "So... guns don't kill people: people kill people, right?" in as nasty-cheerful a voice as you can manage. Then, when they're still wincing, follow up with "And decent people don't let that fact become an excuse."