This story can't be true, since Mexico is a gun control utopia, and in a prison you'd think the authorities could enforce gun control laws. Eric Holder has been out of office for awhile so he probably didn't send any in. Our leaders tell us that where guns are outlawed mass murders don't take place. And they wouldn't lie to us would they?
Of course there's the Rwanda genocide, where a million people were butchered in about a hundred days, most of them hacked to death with machetes or killed with other primitive weapons. That's ten thousand a day, or over 400 an hour (7 per minute), 24 hours a day nonstop, in a nation a fraction the size of America. I don't know how that could have happened, since Rwanda had gun control.
And I guess people never killed each other before guns were invented.