Why On Earth Was Jared Loughner Able to Buy an Automatic Weapon?

As intimated in a prior post, I am a strong supporter of strict gun control and severe limits on who can purchase automatic weapons. I suspect the Founding Fathers - experienced only with muskets and flintlock pistols - never contemplated mentally unbalanced individuals or those out to attack public officials being able to secure automatic weapons that could slaughter or wound dozens of innocent people in moments. Yet the loons who cling to the 2nd Amendment could care less - even though under Justice Scalia's recent analysis of the Constitution (i.e., that women and gays have no protections because the founders did not grant it) gun owners should apparently be limited to flint lock muskets and pistols since modern weapons were unknown to the founders. The Washington Post has highlights from e-mails by a former classmate of Loughner that are horrifyingly accurate in their prediction of Loughner's actions. Here are highlights from the Post article:
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In early June, Lynda Sorenson, 52, had gone back to community college in Tucson in hopes of getting back on the job market. One of her classes was a basic algebra class--and one of her classmates was Jared Loughner, now identified by authorities as the man who killed six people and critically wounded Rep. Gabrielle Giffords (D-Ariz.) in a shooting rampage Saturday. Sorenson's e-mails to friends from last summer, provided to the Washington Post, reveal her growing alarm at Loughner's strange and disruptive behavior in class.
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From June 1, the first day of class:"One day down and nineteen to go. We do have one student in the class who was disruptive today, I'm not certain yet if he was on drugs (as one person surmised) or disturbed. He scares me a bit. The teacher tried to throw him out and he refused to go, so I talked to the teacher afterward. Hopefully he will be out of class very soon, and not come back with an automatic weapon."
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From June 10:"As for me, Thursday means the end to week two of algebra class. It seems to be going by quickly, but then I do have three weeks to go so we'll see how I feel by then. Class isn't dull as we have a seriously disturbed student in the class, and they are trying to figure out how to get rid of him before he does something bad, but on the other hand, until he does something bad, you can't do anything about him. Needless to say, I sit by the door."
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From June 14:"We have a mentally unstable person in the class that scares the living crap out of me. He is one of those whose picture you see on the news, after he has come into class with an automatic weapon. Everyone interviewed would say, Yeah, he was in my math class and he was really weird. I sit by the door with my purse handy. If you see it on the news one night, know that I got out fast..."

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Gun control laws need serious revision so that more mass shootings do not occur.